If I had been in a more pedantic mood, that headline would have more-properly read: "And Then There Were Fifty-Two," but that doesn't really have the same ring to it. Whichever math you prefer, there is now a solid majority in the Senate to pass the House's measure rescinding President Trump's "national emergency" declaration at the southern border. A fifth Republican senator, Mike Lee, just announced he'll be voting for the measure, which means there are already 52 votes for it in advance of tomorrow's floor vote. This should assure its passage, and will likely lead to the first presidential veto of Trump's tenure in office.

It's worth a look at how we got here and what might happen next. Before Trump actually made his reckless designation, there were plenty of Republican senators warning him not to do so -- warning him he would be trampling on the Constitution's separation of powers. Executive overreach has long been a bugaboo on the right, so this position was entirely consistent with their previous complaints about Barack Obama. Many, including Senate Majority Leader Mitch McConnell, strongly urged Trump not to do it.

He ignored them, and went ahead and did it anyway, mostly to deflect attention from the abject failure of his government shutdown strategy. Suddenly, senators from McConnell on down were singing the praises of Trump's "national emergency" move. They were exposed for all to see as flaming hypocrites on what was supposed to have been one of the most bedrock tenets of conservatism. One can only hope this will eventually come back to bite them in the future, when a Democratic president does something they don't approve of.

But while most of the GOP senators had swallowed their long-held beliefs in favor of toadying up to the man who had forcibly taken over their party, a few held firm. Lisa Murkowski and Rand Paul made their stand because they held to their own principles and could see how this might work against them in the future. Two other Republicans also said they'd be voting for the measure, but their motives are a wee bit suspect because both Thom Tillis of North Carolina and Susan Collins of Maine have to run for re-election in 2020 in states that are trending purple, if not blue. So there was a degree of self-preservation in their announced voting stances.

But today's news was the most significant, because it might just free up other Senate Republicans to follow suit. The measure was already likely to pass, since the four GOP votes would be added to the 47 Democrats to make a majority of 51. But that's a pretty thin margin, so an extra vote means the measure is now almost guaranteed to pass. This could free up other Republicans still sitting on the fence, because from now on, nobody's vote can be seen as "the deciding vote."

Senator Mike Lee of Utah was actually trying to engineer some sort of end-run around the contentious vote, up until today. He was going to introduce a measure which would have curtailed presidents in the future from rash national emergency declarations. Instead of the way it works now, any such designation by a president would have to get a majority vote in both houses of Congress in 30 days, or else it would be rescinded. This did nothing to address the current situation, but somehow it was supposed to be a vehicle to convince the four GOP defectors to change their vote. Notably, Thom Tillis was reportedly considering doing so, which could have avoided Trump having to veto the measure.

These backroom machinations fell apart today, however, when Trump called up Lee on the phone during lunch and told him that Trump did not support the new bill Lee was planning on introducing. Without Trump's support, the bill would go nowhere, of course. This yanked the rug out from under Lee's attempt to have some sort of face-saving vote, and in response Lee immediately announced he'll be voting for the original measure tomorrow.

What's interesting, though, is how the other senators that Lee was talking to will react. Lee was, after all, leading this effort, so his defection signals to all the others in the group that it'd be fine if they voted against Trump too. We'll see, when the vote is counted, whether this means the measure gets 53, 54, or 55 votes rather than just 52. There are several other Republican senators (Marco Rubio, most prominently) who loudly denounced the idea of Trump declaring a national emergency before he did so, but who have been awfully coy since then about which way they're going to vote. They haven't added their names to the list of "yea" votes, but then again neither have they said explicitly that they'll vote against it, either. With Mike Lee now signaling that it's OK for them to follow suit, they may just decide to vote for their constitutional principles after all.

Of course, even if there is a miniature rush to vote for the measure among GOP senators, no one in their right mind expects that it will get anywhere close to the 67-vote threshold that would be necessary to overturn a presidential veto. So what will happen after tomorrow is that Trump will veto the measure, and Congress will not be able to overturn his veto. The entire fight will move to the courts, but the congressional vote may be important in these court cases. After all, majorities in both houses -- including one where Republicans are in control -- will have expressed their will that Trump is overstepping his constitutional bounds. Trump will not be able to claim congressional support even in the abstract, because they will have explicitly voted against his move. This could help the legal case of those challenging Trump's declaration.

No matter what happens in the end, though, tomorrow's vote will indeed be historic. For the first time, a president tried to declare a "national emergency" when there was none. For the first time, a president tried to negate the congressional "power of the purse" in blatant fashion. And for the first time, Congress will use the power within the National Emergencies Act to vote their disapproval of a presidential "national emergency" declaration. This has never happened before, because previous presidents respected the boundaries of the law. What's most groundbreaking in all these "firsts," though, is the fact that Republicans are finally beginning to stand up to Trump's excesses. They were forced to do so because Democrats control the House, but nevertheless there is a new schism within the Republican Party between Trump and some of the members of his own party in Congress. That could wind up being the most important "first" of all.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant