Former US Speaker says he's never worked with a more ‘miserable son of a b----' than Republican hopeful Ted Cruz

A former US Speaker of the House has characterised Republican hopeful Ted Cruz as "Lucifer in the flesh".

John Boehner claimed he got along with most people, but had found Cruz "miserable".

"I have Democrat friends and Republican friends. I get along with almost everyone, but I have never worked with a more miserable son of a bitch in my life," Mr Boehner told student newspaper The Stanford Daily.

Mr Boehner presided over a volatile period in Congress, including a partial-shutdown of the US federal government in 2013.

The 16-day shutdown was driven by many of the Tea Party conservatives who now support Cruz's presidential campaign.

Cruz told reporters on a campaign stop in Fort Wayne, Indiana that he had never personally worked with Boehner, who stepped down as speaker last October.

"The truth of the matter is I don't know the man," Cruz said.

"I've met John Boehner two or three times in my life. If I have said 50 words in my life to John Boehner, I would be surprised.

And every one of them has consisted of pleasantries - 'Good to see you Mr Speaker'. I've never had any substantive conversation with John Boehner in any respect," he said.

The stoush comes at a time in which the Washington Post reports elite Republicans are now resigned to accepting Donald Trump as their presidential nominee.

Two prominent Republican establishment congressmen – Bill Shuster of Pennsylvania, who chairs the House Transportation Committee, and Jeff Miller of Florida, who chairs the House Veterans' Affairs Committee – endorsed Trump on Thursday.

"It's time for our party to unite behind Donald Trump and focus our time and energy on defeating Hillary Clinton," Shuster said in a statement.