Washington - The political sway of former U.S. President Donald Trump over Republican Party politics 16 months after he left office is being tested again Tuesday as his preferred candidates face off with Republican opponents in party primaries in key states.

Five states are holding Republican and Democratic primaries, but political analysts will be paying particularly close attention to Trump's fortunes in two states - Pennsylvania in the eastern U.S., which Trump lost in his reelection bid in 2020 after winning there in 2016, and the mid-Atlantic state of North Carolina, which Trump won in 2016 and two years ago.

While winning voter approval this year for many of his endorsed candidates for lower-level offices, Trump has split in two higher-profile contests in the past two weeks.

Author J.D. Vance, his choice in the midwestern state of Ohio for a Republican Senate nomination, won. But his choice for the Nebraska gubernatorial nomination, business executive Charles Herbster, lost.

FILE - Mehmet Oz, a Republican candidate for U.S. Senate in Pennsylvania, meets with an attendee during a visit to a car show in Carlisle, Pa., May 14, 2022.

In one key race in Pennsylvania on Tuesday, Trump has endorsed celebrity television doctor Mehmet Oz to be the party's Senate candidate in the November election for a seat left open by the impending retirement of Republican Senator Pat Toomey.

Oz, who holds dual Turkish and American citizenship, would be the first Muslim U.S. senator. But he is facing stiff competition from David McCormick, a former hedge fund executive and undersecretary of the Treasury for international affairs during former President George W. Bush's administration, as well as from Kathy Barnette, a conservative commentator and author who has surged in polling in the contest.

The three candidates are believed to be in a virtual dead heat heading into the balloting.

The Club for Growth, a national anti-tax group that has often aligned itself with Trump's picks, pumped $2 million into a television ad campaign for Barnette, giving her a quick boost among Republican voters.

FILE - Pennsylvania Lt. Governor John Fetterman, who is running for the Democratic nomination for the U.S. Senate for Pennsylvania, greets supporters at a campaign stop in Greensburg, Pa., May 10, 2022.

But Trump took notice, saying over the weekend that she "will never be able to win" the general election matchup against the likely Democratic nominee, Pennsylvania Lieutenant Governor John Fetterman, who calls himself "just a dude" as he campaigns in his favorite clothes - shorts and a hoodie.

At 6 feet, 8 inches tall, he stands out in any crowd. Fetterman halted his campaign several days ago when he suffered a stroke but says he suffered no cognitive impairment and is recovering.

Trump, while attacking Barnette, contended that Oz "is the only one" who can defeat Fetterman.

Trump also has endorsed Republican state Senator Doug Mastriano for governor in a crowded field of Republican candidates. Mastriano, who has staunchly endorsed Trump's false claims that vote fraud cost him another four-year term in the White House, was already leading in polling for the gubernatorial contest when Trump endorsed him.

FILE - Pennsylvania state Sen. Doug Mastriano, R-Franklin, a Republican running for Governor of Pennsylvania, greets a supporter at a campaign stop in Portersville, Pa., May 10, 2022.

But some Republican analysts have voiced fears that Mastriano's views on the 2020 Trump defeat might prove to be too extreme in the November campaign against the Democratic nominee, state Attorney General Josh Shapiro.

But Trump was undaunted by such fears, saying in a statement endorsing Mastriano, "There is no one in Pennsylvania who has done more, or fought harder, for Election Integrity than State Senator Doug Mastriano. He has revealed the Deceit, Corruption, and outright Theft of the 2020 Presidential Election, and will do something about it."

In North Carolina, Trump nearly a year ago endorsed Congressman Ted Budd as the Republican Senate candidate to fill the seat being vacated by Republican Senator Richard Burr. Budd, according to polling, is comfortably ahead in the contest and is likely to face Democrat Cheri Beasley, the former chief justice of the North Carolina Supreme Court in November.

Trump has also endorsed a conservative firebrand supporter of his, Congressman Madison Cawthorn, for renomination to a seat in the House of Representatives from a western North Carolina district. Cawthorn is facing seven Republican opponents who have attacked his 17-month tenure in office.

FILE - Rep. Madison Cawthorn, R-N.C., speaks before former President Donald Trump takes the stage at a rally in Selma, N.C., April 9, 2022.

Cawthorn has drawn the ire of top Republican congressional officials and has been mired in a string of accusations, such as carrying a loaded gun into an airport check-in line, driving without a valid driver's license and alleging without evidence that he had been invited to drug-infused sex orgies in Washington.

In still another state, sparsely populated Idaho in the western part of the country, Trump has endorsed Republican Lieutenant Governor Janice McGeachin in a gubernatorial primary against incumbent Republican Governor Brad Little.

McGeachin is perhaps best known for seizing on Little's absences from the state to enact her own policy agenda - such as banning mask mandates in schools and public buildings during the height of the coronavirus pandemic - only to have her orders reversed by Little upon his return. She also supports Trump's claim of voter fraud in the 2020 presidential election.