Senate Majority Leader Mitch McConnell, R-Ky., this week underscored — perhaps, contributed to — the peril in which the body’s Republican majority finds itself.

The House vote on a resolution to disable President Donald Trump’s declaration of a national emergency — a vote in defense of the Constitution and in opposition to a hugely unpopular power grab by the president — sends the measure to the Senate. McConnell said he’d support Trump, negating the chamber’s power of the purse.

A measly three Republican senators (Susan Collins of Maine, Lisa Murkowski of Alaska and Thom Tillis of North Carolina) have announced that they will support the resolution, leaving the other 50 Republicans, including 18 of the 22 who will be on the ballot in 2020, in defense of an out-of-control, widely unpopular president. Unless they do an about-face, they’ll all have to answer the painful question: Why didn’t you stand up to Trump and defend the Constitution?

Those deep-red-state voters incapable of thinking critically about Trump might not care, but consider voters in newly swing or downright blue states like Colorado (Cory Gardner), Georgia (David Perdue), Texas (John Cornyn) and Arizona (Martha McSally) where lack of independence from Trump, coupled with a strong performance by a Democratic presidential candidate at the top of the ticket, may put the Republicans at a severe disadvantage.

Even in Kentucky, where McConnell remains overwhelmingly unpopular, you would think a staunch conservative running on fidelity to the Constitution might have a shot in a primary. (I wouldn’t be surprised if McConnell decided to retire, delighted with his handiwork in shaping the judiciary.)

Republicans may get asked some uncomfortable questions about whether they’d allow a Democratic president to declare an emergency in response to climate change or gun deaths. If not, why didn’t they stand up to Trump?

Michael Cohen’s testimony isn’t going to help Senate Republicans either. Imagine the questions Republicans will face on this front:

Why did you not hold a single hearing to investigate Trump’s alleged participation in a criminal scheme to violate campaign laws? Or to investigate lying about his business dealings in Russia? Or about Trump’s financial interests in Saudi Arabia?

If Trump secured his campaign by paying hush money to cover up an affair, and continued the coverup by making payments during the presidency, should he be reelected?

If Trump lied to the American people about doing business in Russia, continued to explore a lucrative deal with the Russians and pulled his punches against Russian President Vladimir Putin to help his chances of getting a deal, should he still be in office?

If someone lies repeatedly, should he be president of the United States? Do you think Trump has repeatedly lied? What about when he denied knowledge of the hush-money payments? When he said the border wall was already being built?

If Trump misrepresented his financial status to banks, should he be president?

Why are you supporting a candidate of Trump’s defective character rather than supporting a different Republican?

Maybe Republicans have good excuses/explanations, but I cannot imagine what they may be. Remember, they will be on the ballot with Trump, defending their own conduct for the last few years and supporting a president with a plane-load of legal and ethical baggage. To be blunt, they’re going to be painted as spineless sycophants who didn’t stop an unhinged president when they had a chance. What’s more, they will have entirely earned that reputation.

Rubin writes opinion for The Washington Post.