Republican presidential candidate Donald Trump has finally heeded the call of party unity to endorse House Speaker Paul Ryan at a campaign rally in Ryan's home state of Wisconsin. Trump had earlier signaled a reluctance to endorse the highest-ranking GOP elected leader, even though Ryan supported Trump from the podium of the Republican National Convention.

When asked earlier about an endorsement, Trump had said that the country needs "very, very strong leadership," implying that Ryan was not such a leader.

Ryan, for his part, hasn't always been 100% behind Trump, criticising him at one point during the campaign for "textbook racism." And after Trump seemed to be withholding his endorsement for Ryan, the House speaker warned that his support for the candidate wasn't a "blank check."

In another strange twist in an already almost unheard of breach in a party, Trump's running mate, Mike Pence, "strongly" endorsed Ryan.

But all was apparently forgiven at a rally in Green Bay, Wisconsin, just days before Ryan's primary election.

"We will have disagreements, but we will disagree as friends and never stop working together toward victory, and, very importantly, toward real change," Trump said, reading a prepared statement. "So in our shared mission, to make America great again, I support and endorse our speaker of the House, Paul Ryan."

He also endorsed Arizona Senator John McCain and New Hampshire Seantor Kelly Ayotte, whom Trump had also indicated he would not back.

"And while I'm at it, I hold in the highest esteem Sen. John McCain for his service to our country in uniform and in public office, and I fully support and endorse his re-election," said Trump, before backing Ayotte.

McCain has been sharply critical of Trump's comments about US Muslims Khizr and Ghazala Khan, parents of a fallen American war hero.

"While our party has bestowed upon him the nomination, it is not accompanied by unfettered licence to defame those who are the best among us," said McCain, a war hero himself whose years of captivity in Vietnam were also once derided by Trump.

The candidate seemed to be mopping up in the last couple of days after a disastrous week.

Before the endorsements, Trump also admitted he in fact did not see a video he had so carefully described at two campaign rallies. He talked of a Iranian government video showing stacks of money paid to the nation by the US. But his campaign said he had misinterpreted a video that actually showed American prisoners from Iran landing in Geneva, Switzerland, which Trump confirmed.

Fox News has been running an Iranian propaganda clip showing a stack of cash that it indicates could be the video that Trump now says he didn't see.