*Former President Donald Trump on Saturday endorsed Doug Mastriano in Pennsylvania’s Republican primary for governor, siding with a candidate who was outside the U.S. Capitol on Jan. 6 and has worked with determination to fully vet allegations of election fraud from the 2020 presidential election.

Mastriano was already leading a crowded field of contenders, and the former president’s endorsement puts him on even stronger footing heading into Tuesday’s primary.

But there are some establishment GOP fears that Mastriano, a state senator and retired U.S. Army colonel, is too extreme to win the general election in November and could drag down other Republicans competing in the pivotal state where a U.S. Senate seat is also up for grabs.

Mastriano has, for example, has fully backed Trump’s election challenges and calls for investigations into election and voter fraud — something Trump hailed in his endorsement statement from his Save America PAC.

“There is no one in Pennsylvania who has done more, or fought harder, for election integrity than State Sen. Doug Mastriano,” Trump wrote. “He has revealed the deceit, corruption, and outright theft of the 2020 presidential election, and will do something about it.”

Trump called Mastriano “a fighter like few others, and has been with me right from the beginning, and now I have an obligation to be with him.”

Mastriano has vowed to take the extraordinary step of requiring voters to “re-register” to vote. Such a move is barred by the National Voter Registration Act and likely runs into significant protections under the federal — and possibly state — constitution and laws, constitutional law scholars say.

“We’re going to start all over again,” he said during a debate last month, referring to registration.