Former President Donald J. Trump on Sunday called Blake Masters, the failed Arizona Senate candidate considering a second run next year, and told him he didn’t think Mr. Masters could win a primary race against Kari Lake, the former news anchor who ran unsuccessfully for governor last year, according to two people briefed on the conversation.
Mr. Trump’s delivery of this blunt political assessment — which could indicate that Mr. Trump may endorse Ms. Lake if she has a relatively open path to the nomination — is at odds with Mr. Trump’s posture so far this political cycle, in which he has shown more restraint in endorsing candidates than he had in the 2022 midterms.
Mr. Trump’s call on Sunday came days after a report that Mr. Masters, a 37-year-old venture capitalist, was preparing to make a second run for the Senate in the swing state after his loss to Senator Mark Kelly, the Democratic incumbent, in 2022.
Ms. Lake, who lost a bitter contest with Gov. Katie Hobbs, a Democrat, is looking at announcing a Senate campaign in the first half of October, two people familiar with the matter said. The race to unseat Senator Kyrsten Sinema, a former Democrat who last year became an independent, is expected to be a crowded one in a state where the Republican Party is fractured.
Last year, Mr. Trump endorsed both Mr. Masters, a political newcomer and an anti-immigration hard-liner who has close ties to the populist New Right, and Ms. Lake, who embraced Mr. Trump’s false claims of a stolen election with particular intensity.
Mr. Masters parlayed Mr. Trump’s endorsement and around $15 million from the billionaire Peter Thiel into a victory in a hard-fought Republican primary. At the time, Republican leaders resented Mr. Trump’s intervention, believing he had propped up a weak candidate.
Mr. Trump went on an endorsement spree ahead of the 2022 midterms, backing several candidates who won their primaries only to go on to lose what Republican leaders considered to be winnable Senate races, including Dr. Mehmet Oz in Pennsylvania, the former football star Herschel Walker in Georgia and Mr. Masters.
By contrast, so far in this cycle, Mr. Trump, the dominant front-runner for the G.O.P. presidential nomination, has endorsed only one Republican Senate candidate who isn’t an incumbent, and it was a safe choice: Representative Jim Banks of Indiana, who is backed by the Republican establishment and is regarded as a lock for that seat.
Mr. Trump’s comparative caution is by design and serves not only his own interests but also those of the same Republican leaders who despaired of his interventions in 2022 midterm primaries.
A spokesman for Mr. Trump, Steven Cheung, said he would not comment on any private conversations “that the president may or may not have had.” Mr. Masters did not respond to a request for comment.
The call between the former president and Mr. Masters was described by two people familiar with it who insisted on anonymity because they weren’t authorized to discuss the private conversation. One of the people said Mr. Trump had not definitively ruled out supporting Mr. Masters’s candidacy and that in conversations with others, Mr. Trump had left open the possibility that Ms. Lake might not run.
In a statement shared by an aide, Ms. Lake said, “I am strongly considering getting in the race and will be making my final decision in the coming weeks,” and cast herself as someone who would be loyal to Mr. Trump in the Senate. Sheriff Mark Lamb of Pinal County is already in the race.
A person close to Mr. Masters who was not authorized to speak publicly stressed that Mr. Masters “believes the party needs a candidate with a proven ability to fund-raise and campaign and is prepared to run in the absence of such a candidate.”
Mr. Masters has told associates that he thinks another “bloody” primary would hurt the party’s chances of winning the seat — and that a battle against Ms. Lake would surely be bloody, according to the person close to him. Mr. Masters has also privately questioned whether Ms. Lake will run, that person said.
The person said Mr. Masters had seriously considered announcing his candidacy shortly after Labor Day but that no plans were set.
Mr. Trump’s skepticism about Mr. Masters long predates their weekend conversation. The former president has told associates he thinks Mr. Masters was a “bad candidate” in 2022, according to two people who have spoken to the former president.
Among Mr. Trump’s complaints about Mr. Masters was that he had tempered some of his comments related to Mr. Trump’s false claims that the 2020 election was stolen from him. When Mr. Masters said in a debate in October 2022 that he hadn’t seen evidence of widespread fraud in the state, Mr. Trump called him, in a moment captured by a Fox News camera.
“If you want to get across the line, you’ve got to go stronger on that one thing,” Mr. Trump told Mr. Masters. “That was the one thing, a lot of complaints about it.” Then he mentioned Ms. Lake, then the Republican nominee for governor.
“Look at Kari — Kari’s winning with very little money,” Mr. Trump said. “And if they say, ‘How is your family?’ She says, ‘The election was rigged and stolen.’ You’ll lose if you go soft. You’re going to lose that base.”
Regardless of Mr. Trump’s motivations, his more cautious approach to endorsements has been appreciated by party leaders. Mr. Trump has told several people that he made too many endorsements in the 2022 midterms — including some for people who have yet to endorse him in his own race for president — and that he plans to be less involved this time, according to two people with direct knowledge of his comments.
Mr. Trump has established a strong relationship with Senator Steve Daines of Montana, the chair of the Senate Republicans’ campaign arm. Mr. Daines’s endorsement of Mr. Trump for president months ago was a strategic move: It gave him entree with the Republican Party’s most influential figure in the hopes of getting him to support the committee’s favored candidates, or at least to refrain from attacking them.
To that end, Mr. Trump has quietly helped Mr. Daines by telling two House Republicans running for Senate — Representatives Matt Rosendale of Montana and Alex Mooney of West Virginia — that he would not endorse them in Senate primaries in their states. In West Virginia, Mr. Daines has issued a statement supportive of a different candidate: the state’s governor, Jim Justice.
A person with direct knowledge confirmed those conversations, adding that part of Mr. Trump’s motivation for delivering the messages was his anger at the anti-tax Club for Growth, a one-time ally that more recently has attacked him. The Club for Growth is spending money to support Mr. Mooney and potentially could do the same for Mr. Rosendale. Mr. Trump’s conversations with Mr. Rosendale and Mr. Mooney were first reported by CNN.
A spokesman for Mr. Rosendale could not be reached for comment.
In a statement attacking Mr. Justice as part of the “big-spending D.C. swamp uniparty,” Mr. Mooney’s campaign manager, John Findlay, noted that “the congressman has endorsed President Trump and would of course like to have his endorsement again.” He added, “As of now, President Trump has chosen to stay neutral.”