Last week, Connecticut became the twelfth state to join the "National Popular Vote Interstate Compact" (usually referred to as the N.P.V. movement), which aims to legally ensure that the presidential candidate who gets the most votes nationwide actually becomes president. This interstate agreement won't take effect until the total number of their Electoral College votes hits 270, which is the number required to win the presidency. With the addition of Connecticut, they have now reached 172, which means they only need to add states with fewer than 100 more Electoral College votes for the plan to become reality.

In concept, the idea is a rather simple one -- each state has passed exactly the same law, which (upon the total number hitting 270) would require all of their electors to cast their vote for the presidential candidate who had won a majority of the national popular vote, no matter how each individual state had actually voted. So if one state voted narrowly for Candidate A, but Candidate B won nationwide, then all of that state's electors would be bound by law to cast their vote for Candidate B instead.

Legally, the idea has not been tested. It probably won't be tested until (1) the magic 270 number is hit, and the compact begins operating as designed, and (2) one state is forced to cast their Electoral College votes for the candidate who didn't win in that state. Up until both of those come to pass, most citizens wouldn't even be aware that the N.P.V. compact even existed, even if they do reach 270 votes. If it goes into effect but doesn't change the actual outcome in even a single state, then the result will be exactly the same as the way things currently work. It'll only become a legal issue when it does change the outcome in at least one of the states that has instituted N.P.V.

From the states which have so far joined so far, this doesn't seem very likely. Here is the full list of states which have passed N.P.V. into law, in the order they joined the compact: Maryland, New Jersey, Illinois, Hawai'i, Washington, Massachusetts, the District of Columbia (treated as a state for the purposes of the Electoral College), Vermont, California, Rhode Island, New York, and now Connecticut. Those are all, obviously, some pretty deep-blue states. In percentage of their own popular vote for president in the last seven elections, these are the most Democratic states in the entire country, in fact. None of these states has voted for a Republican in any of those seven elections (back to Bill Clinton's first victory, in other words). This heavily-tilted bias in which states have passed N.P.V. is a direct consequence of the history of the whole movement, in fact.

From 1800 to 1888, America had four elections in which the popular vote did not match the eventual winner of the presidency (1800, 1824, 1876, and 1888). But since Benjamin Harrison prevailed over Grover Cleveland, the problem didn't reappear until the 2000 election, when Al Gore got more votes than George W. Bush, but lost the presidency anyway. And then, of course, there was 2016, where Hillary Clinton got three million more votes than Donald Trump, but lost in the Electoral College. So after going 112 years without a problem, America has elected two presidents within 16 years that didn't win the popular vote. The 2000 election was what gave rise to the N.P.V. movement, and the 2016 election may have given new momentum to the idea.

In both recent cases, a Republican won the Electoral College while a Democrat won the popular vote. This is obviously why the idea has caught on only in the bluest of blue states, at least so far. But it is doubtful whether enough pure-blue states can push N.P.V. across the 270-vote finish line, because there just aren't really enough of them to do so. To reach the magic number, they'll need at least some purple (or "swing") states to sign up.

The partisan nature of the plan creates another problem for the scheme, though. N.P.V. has been called (by its detractors -- its supporters hate the term) an "end-run around the Constitution." They do have a point. After all, the Electoral College was created and defined by the U.S. Constitution itself. It is rather explicit on the subject, although there are nuances that have appeared that the Constitution does not cover -- like the fact that most states award their electors on a "winner-takes-all" basis, which is not addressed at all in the Constitution. To permanently change the Electoral College (or to get rid of it entirely) would seem to require a constitutional amendment. The N.P.V. would essentially change the way the Electoral College operates without having to cross the incredibly high bar of amending the Constitution. This was by design, whether you call it an end-run or not. It's a lot easier to get enough states to have 270 Electoral College votes to pass N.P.V. than it would be to convince three-fourths of the states to ratify a new amendment.

Seeing as how all the states that have so far signed up are heavily Democratic in their presidential voting, it would seem that the N.P.V. would only kick in if a rather surprising outcome happened -- a Republican wins the popular vote, but doesn't win a majority of the Electoral College votes (under the current system). This would mean all those solid-blue states would be legally bound to cast their Electoral College vote for the Republican candidate -- which wouldn't exactly go over well in places like California or New York. So the initial court challenge to the scheme may actually come from the same Democrats who passed it into law. Stranger things have happened in politics.

This could change if some swing states or even Republican states join the effort, of course. Currently, N.P.V. is under consideration in the legislatures of five more states. One (Minnesota) is another solidly-Democratic state, but the other four are a lot more purple: Missouri, North Carolina, Ohio, and Pennsylvania. Even if all five did join the compact, though, it would only add another 80 Electoral College votes, for a total of 252. So even getting close to the magic number is going to require some swing states to get on board, and getting over the top will likely mean at least six or seven states approve the idea which are not reliably-Democratic states. That will obviously give the movement a lot more political legitimacy, since doing so would mean at least some bipartisan support.

The movement may never reach the goal of 270 votes until the opposite of the 2000 and 2016 elections happens, though -- a Republican candidate wins the popular vote but loses in the Electoral College. This would immediately make the idea a lot more popular in the reddest states, for obvious reasons. If enough of them joined the compact, then N.P.V. could become reality soon afterwards. If such an election did happen, though, it might even spur an actual constitutional amendment, since both sides of the aisle would have been recently burned by the Electoral College vote.

As for the constitutionality of the N.P.V. scheme, nobody will really know until the Supreme Court weighs in -- which would mean that the compact had reached the goal of 270, had been used in a presidential election, and had also overturned the results in at least one state. Up until all of those things happened, nobody would have legal standing to challenge the law.

How the high court would see the scheme is anyone's guess, really. The law already allows individual states a lot of leeway in how they apportion their Electoral College votes. Two states (Maine and Nebraska) have rejected the "winner-takes-all" approach, and instead award their Electoral College votes by giving the overall state winner the two votes that represent their senators, but the remaining Electoral College votes are determined by which candidate wins each House district within the state (which can lead to split Electoral College votes from a single state).

Democrats have been lucky, so far, that a different Republican-led effort has failed to gain any traction in the statehouses. Rather than joining N.P.V., several state legislatures have toyed with the idea of changing their state law to a similar system as Maine and Nebraska use (or other somewhat-proportional splitting of the state's Electoral College votes). If enough swing states did pass such laws, then it would be a lot harder for a Democratic candidate to win the presidency -- which is why Democrats have been so lucky so far that none of these has actually become law. If Ohio and Florida changed to proportionally dividing up their Electoral College votes, Democrats would have to work a lot harder to reach 270, to give just two big examples.

Plenty of people have proposed either completely abolishing the Electoral College (going to just a nationwide popular vote for president), or making other changes to it in the past. But nothing much has come of any of these efforts. The 2000 election changed such arguments from wonky moot points to being a lot more significant, though. Trump's win in 2016 made it all the more relevant. So far, the N.P.V. movement has been the most successful effort to effect change, since it has moved far beyond being an interesting subject to debate in a theoretical way to becoming actual state law in roughly one-fourth of the states. That's impressive. It has taken years of effort and dealing with multiple state legislatures. The N.P.V. legislation has been at least introduced as a bill in all 50 states. In 11 states, these bills have been passed by at least one chamber of the statehouse, but have then failed to make it into law. Some of these states are quite red, as well (such as Oklahoma and Arkansas). All of this represents a monumental effort that has achieved far more success than any other recent scheme to change the way presidential elections work.

If N.P.V. does eventually reach their 270-vote goal (and if it survives the inevitable court challenges), then the Electoral College will become a complete anachronism. If N.P.V. works as designed, then it simply won't matter how many Electoral College votes the winner racks up, because just by winning the national popular vote they'll have guaranteed themselves victory within the Electoral College. This will become bigger news when and if the N.P.V. movement gets a lot closer to that 270 goal, but even now it's admirable to see how the folks behind it have achieved even partial success so far. A lot of people talk about changing the election system America uses in abstract ways, but the N.P.V. movement is slowly making progress towards achieving their goal. And now they're within 100 Electoral College votes of seeing their idea become reality.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant