“If these allegations are true,” Senate Majority Leader Mitch McConnell, R-Ky., said Thursday, “he must step aside.”

That was the typical Republican reaction to the accusation that Roy Moore, Alabama's GOP nominee for the Senate, sexually accosted a 14-year-old girl when he was a local prosecutor decades ago.

This is the most reasonable position. A child sex predator does not belong in the Senate and certainly does not deserve the support of the Republican Party. Second, there’s got to be some presumption of innocence. Whether the accusation is of sexual assault, public corruption, or anything else, an accusation is not proof and cannot be a conviction.

But the problem with the “if true …” position adopted by almost all Republicans is that there is no way to prove guilt or innocence one way or the other. It is Moore's denial against the woman's accusation. The sexual assault and other dubious behavior reported in the Washington Post is alleged to have happened decades ago. The statute of limitations has expired. There will be no criminal investigation.

So we are left with Moore's categorical denial and the Post's well-sourced story, which contains corroborating accounts from contemporaneous friends and public documents.

Senate Republicans should dig deeper and press Moore harder. Although Moore has flatly denied the charges, his response has been mostly to attack news media and his political enemies.

Republican senators, both leadership and those such as Mike Lee and Ted Cruz who endorsed Moore early, ought to demand that Moore back up his denials with something more substantial. He should repeat his claim of innocence under oath, with his hand on the Bible. Handily, Lee and Cruz are both attorneys, and they should conduct an extensive and exhaustive interview.

Did Moore ever have any sort of sexual encounters with minors? What exactly were his interactions with the 14-year-old girl? Are there other women? Are there other stories that will come up?

Nothing will guarantee the party gets the whole story, but perhaps Moore will manage to persuade his future colleagues if he is under oath with God as his witness. If Moore can swear he is innocent, or, even better, provide an alibi, exculpatory witnesses, or evidence, Republican leaders ought to defer to the democratic process.

Until they get this sort of cooperation from Moore, Republicans are right to deny him funds from the National Republican Senatorial Committee. He who pays the piper calls the tune, and if Moore makes himself the client of the NRSC by expecting and taking its money, he has to give something in return more than flat denials. If he admits to anything criminal or even an abuse of power, the party needs to disown him and fund a write-in campaign, probably for Sen. Luther Strange.

Anyone who worries that a write-in candidate could play spoiler and tip the seat to the Democrat needs to ask whether one more vote is an appropriate price for defending a man who can’t swear on the Bible he didn’t sexually accost a 14-year-old girl.

Republicans have accused Moore’s Republican critics of “unilateral disarmament.” The argument is that Democrats’ stuck behind their Barney Franks and Bill Clintons, so Republicans shouldn’t give in.

But the Democrats were wrong to do so. Conservatives were right to say this sexual license and partisan protection eroded the Democrats moral standing. They — we — were right then. We should be right now. Win or lose.