This republican candidate to challenge Trump in US prez election in 2020

Former Massachusetts Governor Bill Weld, a fiscally conservative but socially liberal Republican has called Donald Trump a "schoolyard bully" and said the US president has left the nation in "great peril."

Former governor of the US state of Massachusetts William (Bill) Weld became the first Republican to announce a challenge against President Donald Trump in the 2020 presidential primary.

"I'm in!" Bill Weld tweeted on Monday. The former governor has called on Americans to stand up against the "schoolyard bully" in the Oval Office.

Weld had previously run for office in the US, as a candidate for vice president on the Libertarian Party ticket in 2016, with presidential candidate Gary Johnson.

The 73-year-old is hoping to channel Republican discontent with Trump, despite the president holding a commanding approval rating among registered Republicans and continuing to be favored by the party's core base.

Weld is considered fiscally conservative but socially liberal. He is known for an unconventional, at times quirky, political style and a long history of friction with the party he now seeks to lead.

He endorsed Democrat Barack Obama over Republican nominee John McCain in 2008, though he later said that had been a mistake.

'A better America'

In a two-minute campaign video, Weld's team highlighted his accomplishments as governor of the more progressive state of Massachusetts from 1991 until 1997.

Among his touted successes were balancing the budget, cutting taxes, cracking down on corruption and helping reform welfare.

The video also criticized Trump's misogynistic comments about women, his mockery of a reporter with disabilities, and his failed campaign promise to have Mexico pay for a wall on the southern US border.

"America has a choice," says the narrator of a video announcing Weld's candidacy. "A better America starts here."

Unusual primary challenge

Weld has accused Trump of leaving the nation in "grave peril" and denounced the president's priorities as "skewed toward promotion of himself rather than for the good of the country."

The former governor's campaign makes Trump the first incumbent president since George H.W. Bush in 1992 to face a notable primary challenge.

No candidate that has gone up against an incumbent president has ever been successful at winning the nomination in the modern era, so Weld will face an uphill battle on his quest to unseat Trump.

But the challenge could have the potential for intraparty strife, which could weaken the incumbent or expose vulnerabilities that would later be exploited by a general election rival.