Republicans’ growing Ken Paxton anxiety: ‘He may not be the best-looking guy.’

Republicans are moving to shore up Ken Paxton’s faltering Senate bid, as party donors’ and leaders’ concerns mount and they privately call for the Texas attorney general to step up fundraising and campaign appearances.

Ken Paxton, Texas’ Republican candidate for Senate, at the GOP’s Midterm Convention in Dallas on Wednesday.A group aligned with the Republican Senate Leadership Fund expects to spend at least $50 million—and likely substantially more—to boost Paxton’s campaign against Democratic candidate James Talarico, a person familiar with the plan said. Anxiety about Paxton follows the Republican Midterm Convention this past week in Dallas, where President Trump made multiple jabs at Paxton’s appearance and voice, before urging voters to turn out for him.

The Texas Senate race is one of the most competitive in the country and defending the seat will be essential for Republicans’ hopes to retain their control of the Senate majority. Polls in recent months have consistently shown the race tied, or with Talarico, a progressive state representative and Bible scholar, leading. A recent AARP poll of likely Texas voters showed 48% supported Talarico, while 44% backed Paxton.

A senior White House official said this week that while they still think Paxton can win the race, he needs to step up and campaign and fundraise more. Trump has privately complained about his performance, complaints that have increasingly spilled into public view as the president repeatedly teased Paxton for being a poor speaker and dresser.

At the convention this week, Trump ribbed Paxton’s appearance and the way he dresses and speaks multiple times.

“Some may not like the way he dresses, I don’t,” the president said as Paxton looked on from the audience. “He may not talk exactly perfectly, and he may not be the best-looking guy I’ve ever seen.”

Frustration inside the White House is growing that Republicans need to spend so much time and money on what should be a safely red seat, the senior official said. After the primary, Paxton spent time in Europe, where tabloids published photos of him with a woman in Iceland and England. Some Republicans have criticized him for not visibly campaigning enough, while his campaign has said he is doing so constantly.

Paxton and his allies have pushed back on accusations that he is not campaigning forcefully enough. After primary rival Sen. John Cornyn publicly called Paxton a lazy campaigner last month, Paxton said in a Fox News interview that he was working “18 hours a day, driving all over the state, raising money all over the place.” His campaign has largely shrugged off the criticisms of his appearance as “Trump being Trump,” someone with knowledge of the campaign’s thinking said.

“Every single day, Ken Paxton is traveling across the state and meeting directly with hardworking Texans, raising the resources we need to win in November, and continuing to build momentum,” spokeswoman Madison Cercy said recently.

Several competitive races will decide which party will control the chamber next year, including in Michigan, New Hampshire, Maine, and North Carolina, among others. But Texas is seen as key and unease is mounting that Paxton’s sluggish performance could dampen Republican voter turnout and harm the party’s chances in down-ballot races across the state. Democrats have gained momentum in several important House races and are favored to take back the House majority, according to several election forecasts.

A super PAC aligned with Trump last week announced a $10 million ad buy to back Paxton. Overall, Paxton has raised just $9 million to Talarico’s $68 million and Republicans have been waiting for the president and other national groups to come to his aid.

Many national party organizations favored Cornyn in the primary race and were dismayed to see Trump back Paxton, who has a history of scandals including an impeachment (and later acquittal), a securities fraud indictment (resolved with a pretrial deal) as well as allegations of adultery (divorce pending).

The growing concerns about Paxton represent a departure for Trump. Before endorsing Paxton in a runoff in May, Trump had read a file about Talarico and concluded he was weaker than the media hype and could be beaten, according to an adviser to the president.

Trump was aware of Paxton’s baggage, the adviser said, but thought if a Republican couldn’t beat Talarico, the candidate would deserve to lose.

But Paxton’s fundraising weakness has become pronounced. Some high-dollar donors were reluctant to come on board, either because they were close to Cornyn, they disliked Paxton’s frequent lawsuits against businesses or they were turned off by his personal issues. Talarico has capitalized on nationwide Democratic excitement at the prospect of winning the party’s first statewide seat in Texas since 1994.

State officials in Texas, meanwhile, are alarmed by polls showing closer-than-usual races across the board, concerned that Paxton could drag down the GOP ticket statewide in a year when voter frustration already favors Democratic momentum.

Still, Trump has stuck by Paxton and called him the country’s best attorney general, despite the insults.

Trump said his team told him not to insult Paxton but he did so anyway. “I’m sorry, Ken. Where the hell is he?” the president said. “I’m so sorry. He’ll never speak to me again, but that’s OK.” Trump made similar comments about Paxton a week prior, saying, “you might not like the way he looks…but he was the best attorney general in the country, perhaps.”

Paxton’s campaign has ramped up its attacks on Talarico in recent weeks, selling his Senate race against Talarico as central to the nation’s future. So far this month, Republicans have spent roughly $22.2 million on advertising in the Texas Senate race, compared with Democrats’ $9 million, according to data from AdImpact.

On Tuesday, Paxton’s campaign released on social media an artificial intelligence-generated video of Talarico targeting past statements Talarico made connecting his progressive positions with Christianity. “James Talarico is weaponizing faith to sell a radical agenda, and he even brags about hating Christianity,” Paxton wrote on X.

During his appearance at his party’s midterm convention Wednesday in Dallas, he positioned Talarico as too progressive for Texans and more befitting to represent a liberal state, like California.

“If we lose Texas, we lose the common sense revolution. If we lose the common sense revolution, we lose America,” Paxton said. “California already has two senators, it doesn’t need a third.”

Write to Terell Wright at terell.wright@wsj.com, Elizabeth Findell at elizabeth.findell@wsj.com and Alex Leary at alex.leary@wsj.com