For Republican candidates this election season, high-speed rail is Enemy No. 1 -- or had better be.

And that's putting some Republicans who once supported the idea in an uncomfortable spot.

Take Republican Assembly hopeful Jim Patterson, for example. On Bullard Avenue, just west of Blackstone, a sign for Patterson's 23rd Assembly District campaign proclaims: "Stop the High Speed Rail Boondoggle."

But a Republican opponent, Fresno attorney David DeFrank, points out that in the 1990s when Patterson was Fresno's mayor he spoke glowingly of the project.

That, Patterson responded, was a different proposal that was to be routed along Highway 99 and paid for with private dollars.

Welcome to the 2012 political campaign, where the state's proposed high-speed rail project has become one of the hottest campaign issues for Republicans from city council right up to Congress.

"High-speed rail is a good [issue] for Republicans," said Los Angeles-based political analyst Allan Hoffenblum, a longtime Republican strategist and author of the California Target Book, which tracks the state's elections.

It is one of those black-and-white proposals, he said, where a Republican can draw a clear distinction with their Democratic Party opponent. Many Democrats -- though not all -- have supported the bullet train plan.

Fresno Democrat Jim Costa, for instance, has been a driving force in the project dating back to his days in the Legislature. He's seeking re-election to Congress in the newly created 16th Congressional District.

John Hernandez, a Fresno Democrat running in the 21st Congressional District, has made high-speed rail one of his campaign centerpieces.

But for Republican hopefuls in the June 5 primary election, being 100% against the train has become a litmus test of sorts.

Already, two of Costa's three Republican opponents have highlighted their opposition to the high-speed rail project on their campaign websites.

At least one Fresno County supervisorial candidate, Larry Fortune, and one Fresno City Council candidate, Steve Brandau -- both Republicans seeking nonpartisan offices -- have cited opposition to high-speed rail in their campaign material.

The most heated exchanges so far seem to be where Republicans are facing other Republicans in partisan races.

In the 23rd Assembly District, for instance, the high-speed rail war of words isn't limited to Patterson and DeFrank.

Patterson points to a January letter written by Clovis City Council Member Bob Whalen -- who is also seeking the seat -- that urged people to listen to all sides of the high-speed rail argument before reaching a conclusion.

Whalen's letter doesn't say he supports the plan. It says, in part, "if you are already a 'no,' don't become an entrenched 'no' (no, regardless of benefit). If you are a 'yes,' don't become an entrenched 'yes' (yes, regardless of the cost)."

Patterson said Whalen needs to be unequivocally against the project.

"If there's anybody who's been the last person to figure out the boondoggle, I think it's Bob," Patterson said. "He ought to have come out against it long ago."

Whalen said he is opposed -- now. He waited for the project's business plan to be released before making his decision. That, he said, was the point of his letter -- wait until all the facts were known.

Patterson has done his own about-face.

In early 1996, when he was mayor, Patterson said: "If the state is serious about putting high-speed rail along the corridor, support is guaranteed. This is one of the singular matters I've dealt with that's had widespread support."