In Philadelphia sports lore, there is a famous phrase: “For who? For what?" In 1995, the Philadelphia Eagles were thought to be one player away from Super Bowl contention. In the offseason they signed the NFL's best free agent, Pro Bowl running back Ricky Watters. In the final minutes of the first game of the season, the Eagles were losing to the Tampa Bay Buccaneers, badly. As Philadelphia marched down the field in search of an irrelevant late-game touchdown, quarterback Randall Cunningham threw a bullet to Watters over the middle. With linebackers closing in on him from three sides, Watters didn't even attempt to catch the ball. He batted it down.

In the locker room after the game, reporters asked Watters about his lack of effort on the play. He replied: "I'm not going to trip up there and get knocked out. For who? For what?"

They are questions Republican office-seekers ought to ask themselves before they endorse Donald Trump.

As a matter of loyalty or principle, why do Republican officeholders owe Trump their support? He has no history in the Republican party or of supporting Republican causes. Quite the opposite—he was, until the day before yesterday, a Democratic supporter of Harry Reid and Nancy Pelosi. If, after her 2008 loss to Barack Obama, Hillary Clinton had registered as a Republican and then won the GOP's 2016 nomination, would Republicans feel duty-bound to endorse her? Of course not. She would still be Hillary Clinton. And Donald Trump is still Donald Trump.

Republicans have not had a presidential nominee who pleased a wide majority of the party in a long while; most of their nominees have been mildly disdained. Yet as imperfect as Mitt Romney and John McCain were, they didn't prompt prominent Republicans to burn their party registration cards. There was never a question of whether to endorse them. The resistance to Trump from within the Republican party is a difference of kind, not degree.

Part of the argument against Trump has always been that it would be impossible for him to unite the Republican party. So far this has proven to be true. Trump seems not just incapable of working with elected Republicans, but uninterested. "I don't think it's imperative that the entire party come together," Trump told Morning Joe. "I don't want everybody." As if to drive home the point, the day after clearing the field, Trump went out of his way to reiterate his theory about Ted Cruz's father being involved in the Kennedy assassination. He called Russell Moore, the head of the Southern Baptist Convention's policy arm, "a nasty guy with no heart!" He flipped on opposing the Democratic campaign to raise the minimum wage and bragged, "I'm very different from most Republicans."

And then, to add insult to insult, Trump lied about Paul Ryan and Marco Rubio. He told NBC's Chuck Todd that he was surprised that Paul Ryan had withheld his endorsement since the speaker of the House had called and congratulated him after the New York primary. Trump told Fox News's Bret Baier that he had several "really nice conversations" with Rubio and that Rubio had been "very supportive, very good."

According to Ryan's and Rubio's staffs, these conversations never happened and Trump's account is fictional. Not the usual way one builds party unity.

President Obama often complains that congressional Republicans reflexively opposed him without ever trying to work with him. To which Republicans reply that Obama was a deliberately polarizing figure who showed no interest in cooperating with the GOP Congress, preferring instead to mock and marginalize them. Trump seems to believe, like Obama, that unity can be demanded, rather than earned.

So as a matter of principle, Republicans owe Trump nothing. Of course, politics is sometimes inhospitable to principle. But even as a crass, electoral concern, it may be foolish for Republicans to support Trump. Understand that the term "Trump supporters" now includes not just the alt-right and the KKK, but every Republican officeholder who has endorsed Trump. If Trump loses in November, he will harrumph back to Mar-a-Lago unbowed. The fact that he will have no future in the party is likely to disturb him very little, since he had no past in it, either. But other Republicans—Bobby Jindal, Rick Perry, Chris Christie, Mitch McConnell—will not have the same luxury.

To endorse Donald Trump is to make your political career hostage to a man who may, at any random moment, accuse a former president of treason. Or encourage his supporters to physically assault their opponents. Or spin wild conspiracy theories, or tell obvious lies, or praise murderous dictators.

One of the oddities of politics is that its practitioners can be destroyed by a single moment. Think of Marco Rubio's New Hampshire debate flub. Or Rick Perry's 2012 mishap. Or Mitt Romney's "47 percent" comment. Or Howard Dean's scream. Or Al Gore's sighing. Yet some politicians can survive anything short of a full-scale nuclear first strike.

Both Hillary Clinton and Donald Trump have survived facts and statements that would have destroyed most politicians. It isn't fair, but fair's got nothing to do with it. Most people running for office do not have electorally the resilience of a cockroach.

Republicans considering whether to endorse Trump should ask themselves, honestly, whether they possess the same imperviousness as Trump. Because they're going to need it. Over the next six months, any Republican running for election who is supporting Trump is going to be importuned to defend every insane utterance, every lie, every dangerous idea that emanates from the man. They're going to be pestered, every day, at every campaign stop, to either endorse or disavow everything noteworthy Trump says.

That's the flip side to the "unity" arguments Trumpkins such as Mike Huckabee are mounting. It's easy for Huckabee to be pro-Trump—he'll never stand before voters again. But people with careers need to understand that there are no good alternatives in a Trumpist GOP, only less-bad ones. The choice isn't whether Republicans unite behind a guy who became a Republican five minutes ago and holds almost no views in common with theirs. It's whether Republican office-seekers should preserve some independence or yoke themselves to a perpetual scandal machine.

Republicans in the past have proved clear-eyed about such things. Remember Todd Akin's 2012 Missouri Senate campaign? Akin was one of those everyday politicians—the kind who can end their career with a single, stupid remark. He chose to dilate on the subject of "legitimate rape" during an interview with a local TV station.

Akin's remarks became a national sensation. Did Republicans rally behind him in "unity"? Akin, after all, had won his party's nomination fair and square. The people of Missouri had spoken! And Akin was an actual Republican: He served in the House of Representatives for more than a decade. He had opposed abortion and supported the Second Amendment and was even in favor of building a wall—or at least a fence—along the Mexican border.

Yet Republicans ran from Akin as if he had the plague. Mitt Romney and Roy Blunt abandoned him. So did Scott Brown in his Massachusetts race and Ron Johnson in Wisconsin. The National Republican Senatorial Committee not only stopped spending in Akin's race, but went so far as to issue a press release highlighting calls for Akin to drop out.

That NRSC press release about Akin makes for fascinating reading today. In it, Sean Hannity, Ann Coulter, and the Wall Street Journal—all of whom have conspicuously demanded Republican "unity" behind Trump—were cited, calling on Akin to give up his legitimately earned Senate nomination and drop out of the race.

The Journal lamented that "Mr. Akin has sunk his own ship." Coulter said that "Republicans can't risk these kinds of mistakes" and that if Akin didn't give up his nomination and withdraw she would "officially" "hate" him. Hannity implored Akin to understand that "elections are bigger than one person." So much for unity.

Any Republican running for office who supports Donald Trump is pledging their honor, their dignity, and their political life to this man. So before they make that choice, they ought to ask themselves: For who? For what?