Des Moines (United States) (AFP) - He wants to help the working poor, enact climate protections and unify Americans, but 2020 Republican presidential candidate Bill Weld saved his sharpest talk Sunday for Donald Trump, branding his rival a racist who could destroy their party.

Weld, a former two-term governor of Massachusetts, is perhaps the White House hopeful with the least chance of getting there.

He is going up against a massive Trump political machine that enjoys the backing of the vast majority of the Republican establishment and the party's lawmakers in Washington.

But the 74-year-old underdog, who was visiting the Iowa State Fair, issued a dire warning to the GOP, saying its representatives in Congress will be doomed if they do not fully repudiate the "absolutely" racist president.

"If the Republican Party in Washington doesn't expressly disavow his racist tirades, they are going to go down to massive defeat in 2020," Weld told reporters after his stump speech to several dozen voters.

The president, he said, has blood on his hands for the mass shooting in El Paso, Texas a week ago that left 22 dead, as the gunman's hateful anti-Mexican manifesto was "torn right out of the Trump playbook."

"So yeah, I specifically link him to the El Paso shooting, but more broadly to the climate that produces all these shootings," he added.

Weld was the lone Republican candidate to address voters this year at the fair, where nearly all of the two-dozen Democratic presidential contenders are making their pitch.

On the soapbox, Weld called Trump a RINO -- Republican in name only -- "because he's not a fiscal conservative."

To reporters afterwards, he let loose, saying Trump and his advisors set out to "divide the country every which way they could," by filling Americans with resentment and hate.

"It's the opposite direction that we need to go in," Weld said.

A few fairgoers in Trump hats listened to Weld's speech.

Afterwards, someone shouted "Trump's not racist!"

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- 'Ignoble' -

Weld's strategy is to campaign in Massachusetts, where he was a popular governor, and other New England states, before heading west to California and Oregon.

He will return to the Mid-Atlantic and finally tackle the Rust Belt states like Wisconsin, Michigan and Pennsylvania that Trump won in 2016.

How can he win? "The main thing is speaking the truth, not lying, not being ignoble, not trying to set people against each other," Weld said.

"And I think the truth about what Mr Trump is now doing and has been doing, is going to sink in," he said.

Weld, who leans libertarian, offered some surprisingly liberal positions.

"The rich are too rich, and the poor are too poor, and that's not good for social cohesion," he said as he discussed how the tax burden for low-income Americans is "really not fair."

He mocked Trump's claims that climate change is a "hoax," described his opposition to voter suppression efforts that have disenfranchised minority voters, and blasted Trump's "inhumanity" on immigration and asylum issues.

Weld is the longest of longshots.

At a poll at the fair, Trump as of Sunday received 97 percent of Republican votes, compared with Weld's three percent.