Opinion writer
Khizr and Ghazala Khan, whose son was killed while serving in Iraq, stood before the Democratic convention on Thursday, July 28 and blasted Donald Trump's rhetoric on Muslims and immigrants. Here's what happened next. (Monica Akhtar/The Washington Post)

THE MORNING PLUM:

Donald Trump’s continuing war with the Khan family — which Trump inexplicably continued to keep in the news this morning with a series of new tweets — raises the specter of a brutal trap for Republicans.

It’s this: If individual Republicans don’t break off their support for Trump’s candidacy now — by, say, withdrawing their endorsements — they run the risk of having no choice but to do so after Trump sinks even further into wretchedness and depravity, to a point of true no return. (Presumably there is such a point.) At that juncture, their move will look unprincipled and desperate, leaving them stained — perhaps irrevocably — with their previous willingness to stick by him during much of his descent, and depriving their break with him of whatever moral force it might have had if done earlier.

As some Republicans are already remarking, Trump’s battle with the Khan family makes it harder and harder to avoid acknowledging the possibility that we really have no idea how low Trump will sink. After Khizr Khan, the father of a soldier killed in Iraq, criticized Trump from the stage of the Democratic convention last week, Trump responded by asking why his wife had stood by silently, unleashing a torrent of criticism from lawmakers in both parties and setting the stage for another round of media appearance by the Khans, in which they brutally tore into Trump’s lack of empathy and temperamental unfitness for the presidency.

Humayun Khan was an American Muslim Army soldier who died serving the U.S. after 9/11. His father, Khizr Khan, spoke at the Democratic National Convention and offered a strong rebuke of Donald Trump, saying, "Have you even read the United States Constitution?" (Video: Victoria Walker/The Washington Post;Photo: Michael Robinson Chavez/The Washington Post)

Trump kept the story going this morning, tweeting angrily that Khan had attacked him (reminding us that Trump, not the grieving father of a fallen soldier whose religion Trump attacked, is the truly aggrieved party here) and that this story is not about Khan but is rather about “RADICAL ISLAMIC TERRORISM.”  Republicans who have long warned their own party against embracing Trump are noting that this episode shows we are only seeing the beginnings of how unhinged Trump’s candidacy could become.

“Trump is inevitably going to get worse, not better, as his poll numbers get worse,” Tim Miller, a former adviser to Jeb Bush and a frequent Trump critic, told me this morning. “When he’s being criticized and his back is against the wall, he’s going to act out and become more extreme and despicable. Every time we think he’s gone as low as he’s going to go, he manages to sink even lower. There is no argument for waiting until he behaves better.”

“If Republicans are going to have to disavow Trump eventually because of how bad his behavior has gotten,” Miller continued, “it is incumbent on them to get the political benefit of doing it when it’s a principled stand, rather than waiting until they are backed into a corner and there’s no other choice.”

Take the response of House Speaker Paul Ryan. Over the weekend he issued a statement declaring that “many Muslim Americans have served valiantly in our military” and their sacrifice “should always be honored.” But his statement did not mention Trump at all. Ryan has previously said with real eloquence and sincerity that the GOP “stands for” the idea that there are “many Muslims serving in our armed forces” and “dying for this country” and in defense of the Constitution and “pluralism and freedom and democracy and individual rights.” But the GOP’s presidential nominee — the man Paul Ryan is trying to get elected president — belittled the religion of a family that made the ultimate sacrifice in defense of all those things, and if elected, would impose a religious test temporarily barring Muslims from entering the country.

Many Never Trump Republicans and conservatives don’t believe Ryan’s position is a tenable one. But the point is that this position on Trump could get harder, not easier, to sustain. As Peter Wehner, a former speechwriter for George W. Bush, put it: “Trump is a man of sadistic cruelty. With him there’s no bottom.” If this is right, and Trump sinks even lower, leaving no alternative but to cut him loose, Republicans such as Ryan will have done so not in defense of their own principles, but because events forced them to.

Now, it is always possible that Trump will not sink any lower and will suddenly improve. But that is now looking like a much bigger gamble than it did before Trump’s war with the Khans began.

One last point: This ongoing battle with the Khan family tests one of the core assumptions Trump has made about this race, which is that he can win the presidency largely through sheer media dominance. As I’ve reported, the Clinton campaign questions this assumption, arguing that even if Trump is very good at sucking up all the media oxygen, the antics he’s resorted to in order to do so will only drive up his negatives further and prevent him from broadening his appeal among key voter groups that will help decide this national election. Trump’s war with the Khans is certainly allowing him to dominate the media. Soon we’ll see whether it’s helping him or doing even more damage.

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* POLL SHOWS CONVENTION BOUNCE FOR CLINTON: A new CBS News poll finds that Clinton now leads Trump nationally by 46-39 among registered voters nationally, up from a tie last week. Note this:

In the wake of the Democratic convention, positive views of Hillary Clinton have risen five points among registered voters, from 31 percent a week ago to 36 percent today. Unfavorable views of Hillary Clinton have dropped six points: from 56 percent to 50 percent.

The polling averages now show Clinton up slightly more than four points nationally, with Trump still stuck just under 43 percent.

* MORE REPUBLICANS RIP TRUMP: Now Republicans from swing states and districts, such as Sen. Kelly Ayotte of New Hampshire and Rep. Michael Coffman, are slamming Trump for belittling the Khans. Ayotte professed herself “appalled,” while Coffman said: “Having served in Iraq, I’m deeply offended when Donald Trump fails to honor the sacrifices of all of our brave soldiers who were lost in that war.”

Trump’s antics will probably only get worse, prompting more and more vulnerable Republicans to hammer away at him, perhaps driving him towards more crazy antics.

* JOHN McCAIN JOINS THE CHORUS: The Arizona Senator hits Trump, stating flatly that he “disparaged a fallen soldier’s parents”:

“I cannot emphasize enough how deeply I disagree with Mr. Trump’s statement. I hope Americans understand that the remarks do not represent the views of our Republican Party, its officers, or candidates….I’d like to say to Mr. and Mrs. Khan: thank you for immigrating to America. We’re a better country because of you. And you are certainly right; your son was the best of America, and the memory of his sacrifice will make us a better nation — and he will never be forgotten.”

So McCain agrees with the Democratic nominee, who has also said that the slain Khan represents “the best of America.”

* GOLD STAR FAMILIES RIP TRUMP: CNN reports that a group of Gold Star families has penned a letter to Trump demanding an apology for his “anti-American” comments:

“Your recent comments regarding the Khan family were repugnant and personally offensive to us,” the group of 11 “Gold Star” families wrote. “We feel we must speak out and demand you apologize to the Khans, to all Gold Star families, and to all Americans for your offensive, and frankly anti-American comments.”…”Ours is a sacrifice you will never know. Ours is a sacrifice we would never want you to know,” the families wrote in the letter.

Trump has made a lot of sacrifices. Really big, impressive, tremendous ones.

* TRUMP SUPPORTERS SMEAR THE KHAN FAMILY: The Post overview of the escalating battle between Trump and the Khans serves up this distasteful nugget:

Late Sunday, Trump supporters, including longtime adviser Roger Stone, circulated unsubstantiated accusations from an anti-Islam website about Khizr Khan. Stone tweeted a link to a post that, among other things, accuses Khan of being a Muslim Brotherhood agent who wants to advance sharia law.

How long until Trump goes there?

 * IT’S GUT-CHECK TIME FOR GOP POLITICIANS: E.J. Dionne frames their dilemma:

Republican politicians face a choice. They can accept Hillary Clinton’s invitation to abandon Donald Trump and prevent a redefinition of their party as a haven for bigotry. Or they can prop Trump up, try to maximize his vote — and thereby tarnish themselves for a generation….Every Republican politician and commentator who continues to say that Trump is a superior or even morally equivalent choice to Hillary Clinton will now own their temporary leader’s brutality for the rest of their political careers.

And as we noted above, this could only get worse from here — perhaps even a lot worse.

* AND SALES OF POCKET CONSTITUTION SKYROCKET: During his convention speech, Khizr Khan brandished a pocket Constitution and urged Trump to read it. Americans responded thusly:

Now, sales of the little book are skyrocketing. A $1 edition of the pocket Constitution printed by the nonpartisan National Center for Constitutional Studies became the second best-selling book on Amazon. It remains there today. It’s not just sales; Google searches for the document increased more than ten-fold on Friday compared to the daily average of the previous month.

It’s an interesting turn of events that a Muslim-American family responding to the nominee of the party of Very Serious Constitutional Conservatives may have successfully stoked public interest in our founding document.