Let’s run down what has happened just in the past couple of days:

Sen. Susan Collins (R-Maine) wrote an op-ed in today’s Post that begins, “I will not be voting for Donald Trump for president.” That brings the number of Republican senators refusing to back Trump to six, though on the bright side, there are still 48 left who haven’t yet defected.

Fifty prominent national security officials who held positions in previous Republican administrations released a letter proclaiming their opposition to Trump, saying, “We are convinced that in the Oval Office, he would be the most reckless President in American history.”

Former CIA director Michael Morell, who served under both Republican and Democratic presidents, endorsed Clinton, saying “Donald J. Trump is not only unqualified for the job, but he may well pose a threat to our national security.”

Two former Republican Environmental Protection Agency administrators endorsed Clinton, saying Trump has shown “a profound ignorance of science and of the public health issues embodied in our environmental laws.”

A former Republican governor of Michigan and a former Republican senator from New Hampshire announced their support for Clinton.

A bunch of other less well-known former Republican officials announced their support for Clinton.

The communications director of the Florida Republican Party quit , saying he could not in good conscience advocate the election of Donald Trump.

It would be easy to say that these people are only jumping ship after a wave of bad poll results or that they’re the ones who have little to lose (Collins, for instance, gets reelected in Maine because of her carefully cultivated reputation for moderation; supporting Trump could damage that reputation). And that would be true. But even if none of these defections represents an inspiring profile in courage, their political significance is still profound.

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That’s because it’s one thing when you have one or two defections, but the more they start to pile up, the more likely further defections become, each one giving momentum to the next. No one wants to be a lonely voice going against the consensus of his or her party, but once there’s a critical mass of defectors, it becomes much less socially and politically threatening to take that stand. Instead of isolating yourself by defecting, you’d be joining a group, and one whose members don’t see themselves as having abandoned the party they love.

At the moment, the defectors aren’t well known to most voters; it would be a much bigger story if someone like House Speaker Paul Ryan (R-Wis.) endorsed Clinton, which is obviously not going to happen. But as more and more of these announcements pile up, Republican officials may start asking themselves not just “How are voters going to react if I don’t stand behind our nominee?” but “How am I going to look if so many other Republicans defected but I didn’t? Are voters going to think I was cowardly and unprincipled?”

If Trump continues to trail badly in the polls, that changes the calculation as well. Up until now, elected officials making this calculation would wonder what would happen if they defected and Trump won. Would they get a primary challenge from the right? Would the Trump administration shut them out? Those could be serious consequences. But if Trump winning looks like a remote possibility, then a different scenario looms much larger: Trump loses, the party descends into recriminations, and who comes out looking good? It might well be those who refused to back him, and did so as early as possible.

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At the very least, those who would wind up looking the worst would be people like Marco Rubio or Rick Perry, who made dark warnings about what a disaster Trump would be for both for the party and the country, and then came out and gave him their hearty endorsements anyway. Even those who don’t defect will have an incentive to be as critical of Trump as they can in public, essentially taking the Paul Ryan position, which comes down to: I hate everything he says and believes, but he still has my support.

All that trickles down to the voters by giving moderate Republicans permission to withhold their votes from Trump, either by voting for Clinton, voting for a third-party candidate or not voting for president at all. And it could convince lots of independents that one of those choices is the independent thing to do, since only the most ardent Republicans seem to be sticking with their toxic candidate.