The stream of down-ballot Republicans breaking with the Trump campaign over Mr. Trump's past vulgar language has now been capped by the notice from House speaker Paul Ryan (R-Wis.) that "he will not defend or appear with" Mr. Trump, and that "rank-and-file" Republicans are on their own "to do what's best" in their districts.

Ryan's counterpart in the Senate, Majority Leader Mitch McConnell (R-Ky.), for his part, is giving the presidential campaign controversy the silent treatment: "I don't have any observations about it."  But The Hill observes:

More than a dozen senators have either rescinded their support of the GOP nominee or called on him to step aside[.]

Republicans jumping on and off the Trump ship is nothing new, but the tactic may expose some Republican candidates to another danger, at least according to the National Journal's Josh Kraushaar, who asks if the "Republican panic was premature" in light of Mr. Trump's strong debate performance:

And the squeamish Republicans who broke with the ticket over the weekend – despite having backed Trump through all his myriad previous controversies – will be waiting in political purgatory, hoping that Trump's voters will still support them down the ballot.

… After the Trump tape leaked Friday afternoon and generated non­stop cable-news coverage, many Republicans had a collective panic attack. Instead of waiting to see polling on how voters would react, many chose to cut bait with their nominee.

… Republican party leaders have been grappling with an uncomfortable reality: Their most reliable voters are entirely disconnected from the GOP leadership. The grassroots don't interpret these controversies the same way as the party elite.

Mr. Kraushaar illustrates the point by citing a weekend poll indicating that 74% of Republican respondents want "party officials to continue to stand by Trump" and by noting that "several top Republican elected officials" were booed when they publicly renounced Trump over the weekend.  The author also reminds readers of the political cost to Senator Ted Cruz (R-Texas) for not endorsing Donald Trump at the convention.

Mr. Kraushaar ominously suggests that "Trump supporters could punish new defectors ... by leaving the down-ballot portion of their ballot blank."  The fracturing in Trump's down-ballot support could thus have devastating consequences, according to Mr. Kraushaar:

But now the GOP has to worry that by impulsively breaking their Faustian bargain because of a decade-old videotape, they may have cost themselves control of the Senate.

As for Senator Cruz, he says he is still in for Donald Trump because he thinks "Hillary Clinton is an absolute disaster."  A disaster that would be compounded by the loss of the Senate and any potential firewall against Hillary Clinton's Supreme Court nominees.