WASHINGTON (NYTIMES) - When Representative Ryan Costello of Pennsylvania announced on Sunday (March 25) that he would join more than 40 other congressional Republicans not seeking re-election in November, he left no doubt about the reason: President Donald Trump's conduct made it impossible to talk about anything else.
Were he running, Costello said in an interview, he would be inundated with questions about Stephanie Clifford, the pornographic film actress known as Stormy Daniels, who has said she had an affair with Trump and was threatened to stay silent about it.
"If I had a town hall this week, it would be question after question," Costello said. "'Do you believe him or do you believe her? Why don't you believe her?'"
While Republicans have been bracing for months for a punishing election in November, they are increasingly alarmed that their losses might be even worse than feared because the mid-term campaign appears destined to turn more on the behaviour of the man in the White House than any other in decades.
As much as gun control, immigration, the sweeping tax overhaul and other issues are mobilising voters on the left and the right, the seamy sex allegations and Trump's erratic style could end up alienating crucial blocs of suburban voters and politically moderate women who might be drawn to some Republican policies but find the president's purported sex antics to be reprehensible.
Polls and every recent election show that Trump has galvanised liberal and moderate voters - especially women and those with college degrees - to oppose his party. Yet at the same time, personal loyalty to the president is increasingly the most crucial litmus test for Republicans.
This widening chasm has created a dilemma for Republicans, especially in liberal and swing states.
If they stay faithful to Trump they risk incurring the wrath of many in the political centre during the general election, likely dooming their campaigns. But if they disavow the president, they risk depressing turnout from their core Republican voters and watching their pool of volunteers evaporate overnight.
"It's a political Catch-22," J. Tucker Martin, a Virginia Republican strategist, said. "Candidates can't win without their base. But what it takes to satisfy a pro-Trump base in 2018 will make Republican candidates in many states unacceptable to large swaths of the electorate."
And perhaps most ominous for Republicans, there does not appear to be an obvious middle ground: Martin's candidate for governor of Virginia last November, Ed Gillespie, sought to avoid either inflaming or embracing Trump, and he was still soundly defeated.
At this point, many in the party seem more consumed with their nomination contests than with steeling themselves for the general election. And they are trying to finesse awkward topics like Clifford's claims in ways that do not turn off primary voters.
In the two states where Republicans are most at risk of losing Senate seats, the party's leading candidates have aligned themselves with Trump so far, in an attempt to pre-empt a challenge from their right in the primary.
Senator Dean Heller of Nevada and Representative Martha McSally of Arizona, the establishment-preferred Senate candidate there, have praised Trump in ways that Democratic ad-makers could use against them this fall.
Such short-term calculations amount to political malpractice, say Democrats.
"Trump is way more than the proverbial elephant in the room - he's the elephant in the room with political bad breath, B.O. and a foul mouth," said Ace Smith, a veteran Democratic consultant, who argued that the last time a president's conduct loomed so large in congressional midterms was in the post-Watergate election of 1974.
And Democrats believe that Trump so overwhelms the political conversation that it makes their own liabilities pale in comparison.
"I don't see headlines with: 'Porn star sues Nancy Pelosi,'" said Democratic Representative Cedric Richmond of Louisiana, when asked about his party's polarising House leader.
Just as gun control has put many Republican candidates on the defensive after Saturday's student-led demonstrations, Trump's behaviour is increasingly backing candidates into a corner.
At a debate last week, Debbie Lesko, the Republican nominee for the Arizona congressional seat vacated by Trent Franks, said that Trump "needs to address" the claims of sexual impropriety against him.
"I don't know that he can lead on that issue, but he certainly needs to deal with it and it has to be investigated," said Lesko, a recent state senator, adding: "I don't use his rhetoric, and I'm certainly not going to sexually harass anyone."
But in an illustration of how firm Trump's grip is on the party base, the president's past comments about groping women have become an issue in some races only because pro-Trump candidates are attacking Republican rivals for abandoning him over those infamous "Access Hollywood" remarks.
Michigan's attorney-general, Bill Schuette, is assailing his rival for the Republican nomination for governor, Lt. Gov. Brian Calley, because Calley backed away from Trump after the "Access Hollywood" tape came out in 2016.
Indeed, the party's embrace of Trump is most striking in several Midwestern states where he triumphed in 2016, and where a large number of important Senate and governor's races are underway.
In Indiana, three candidates for Senate have each tried to position themselves as steadfast supporters of the White House, and one predicted Trump could earn a Nobel Peace Prize for his outreach to North Korea.
In West Virginia and Ohio, Republican members of Congress running for Senate are boasting of having supported Trump before their states' primaries in 2016.
But even in conservative-leaning Midwestern states, there is a deepening recognition that Trump's volatile persona is a problem.
In Missouri, home to one of the nation's most competitive Senate races, Trump swooped in this month to headline a fundraiser for Josh Hawley, the mild-mannered state attorney general challenging Sen. Claire McCaskill, a Democrat.
Trump used the occasion to brag loudly of having bluffed his way, using made-up facts, through a phone call with Canada's prime minister - a boast that made international news.
Former Sen. John C. Danforth, a senior statesman among Missouri Republicans who is a strong backer of Hawley, called the president a challenging force in the race. Voters, he said, "object to him on the basis of his style and demeanour and the way he talks and acts toward people".
Danforth said he was hopeful voters would distinguish Republicans like Hawley, a cerebral former law professor, from Trump, rather than rejecting "anybody who has the same label Trump has."
But as Costello, the representative not running for re-election in Pennsylvania, noted, Trump's persona did not just fuel liberal activism - it also made it nearly impossible to talk about Republican policy goals.
"He blocks everything out," Costello said of the president. "What fuels the energy isn't the issues. It's the personality."