By WILL WEISSERT
Associated Press

WASHINGTON (AP) - "Never Trump" Republicans are anxious to see the president face a credible primary adversary.

But the party may erect political hurdles that could make challenges that are already the longest of longshots even more difficult.

It's a tough road for a reason: Every incumbent president for four-plus decades who has faced a serious such challenge was weakened enough to ultimately lose reelection.

That encompasses Presidents Gerald Ford, Jimmy Carter and George H.W. Bush. The exception is President Richard Nixon, who survived two primary challengers to cruise to another term in 1972.

Former Massachusetts Gov. Bill Weld has already spent months challenging President Donald Trump.

Former tea party-backed Illinois congressman and conservative talk radio host Joe Walsh announced Sunday that he's joining the race - and others may follow.

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