WASHINGTON -- He can't do it, Republicans. It's time for you to admit that Donald Trump is incapable of even pretending to be an acceptable candidate for president. The question is which side of history you want to be on.

Are you going to stand with him as the balloons drop on the last night of the convention, knowing he shares neither your views nor your values? Are you going to work your hearts out this fall to put an unstable bully in charge of our national defense? Is party unity so much more important to you than trifles such as responsibility, duty and honor?

Leading Republicans should pay attention to what Sen. Mike Lee told a reporter for the conservative Newsmax website: "What I am saying is Donald Trump can still get a vote from a lot of conservatives like me, but I would like some assurances on where he stands. I would like some assurances that he is going to be a vigorous defender of the U.S. Constitution. That he is not going to be an autocrat. That he is not going to be an authoritarian. That he is not somebody who is going to abuse a document that I have sworn an oath to uphold and protect and defend."

Lee, who has not endorsed Trump, specifically mentioned "the fact that he accused my best friend's father of conspiring to kill JFK" -- referring to Trump's scurrilous and unfounded charges about the father of Sen. Ted Cruz -- and also Trump's history of making "statements that some have identified correctly as religiously intolerant."

My only question for Lee is why Trump might still get his vote. I realize that Hillary Clinton is a Democrat, but no one has suggested that she might shred the Constitution or that she is a religious bigot. I thought the oath to "protect and defend" meant putting country before party.

To be sure, some leading Republicans are doing just that. Mitt Romney, the party's 2012 nominee, is one of the loudest and most consistent Never Trump voices. The Bush family, which incarnates the GOP's recent history, is boycotting the convention. My colleague George Will, a principled conservative if ever there was one, said last week he had left the Republican Party because of Trump.

But most GOP luminaries are like Senate Majority Leader Mitch McConnell, who has obvious reservations about his party's presumptive nominee but supports him nonetheless. McConnell said this week that "people are looking for a level of seriousness that is typically conveyed by having a prepared text and Teleprompter and staying on message."

In other words, McConnell hopes Trump can at least pretend to be serious and stable long enough to make it through the general election campaign.

Asked Wednesday if he agreed, Romney said no. "I think Mr. Trump has demonstrated who he is by virtue of what he said in the process to this point," he explained. "What he says from this point forward may paper over that."

I've had the same worry -- that Trump would appear to be more statesmanlike and fool voters into thinking he had changed. With every passing week, however, I become less concerned about this scenario. Trump is who he is.

Every time Trump gives a prepared speech in which he manages to stay on message, drawing praise from the party establishment, he negates it by reverting to his old self. His address on foreign policy a couple of months ago, for example, was wrongheaded but basically mainstream. This week, however, he has been ranting about how the United States needs to use waterboarding and other torture techniques against suspected terrorists.

And you're going to vote for this guy, Sen. John McCain? You, a former POW who was tortured by the North Vietnamese? You, the Senate's most outspoken opponent of the practice?

McConnell said he hoped that Trump "is beginning to pivot and become what I would call a more serious and credible candidate for the highest office in the land." Asked whether this was happening, McConnell replied, "He's getting closer."

But he's not, and McConnell surely knows it. So does House Speaker Paul Ryan, who will preside over the convention at which Trump is set to be nominated. So do many Republicans who, when I ask them about Trump, either sigh, shrug or run away.

We are talking about the presidency of the United States, Republicans. You are about to nominate and support a man you know to be dangerously unworthy. Some loyalty.

(c) 2016, Washington Post Writers Group