Trump stands by false claim Obama founded the Islamic State

Donald Trump today repeatedly accused President Barack Obama of founding the Islamic State group, refusing to take back a patently false allegation even when questioned about the logic of his position.

A day after lobbing the attack against the president during a rowdy rally, Trump pressed ahead during a round of interviews.

The Republican presidential nominee brushed off conservative radio commentator Hugh Hewitt's attempt to reframe Trump's observation as one that said Obama's foreign policy created the conditions in Iraq and Syria that allowed IS to thrive.

"No, I meant he's the founder of ISIS. I do," Trump said, using another acronym for the extremist group that has wreaked havoc from the Middle East to European cities.

Hewitt asked Trump if he would acknowledge that Obama hates the Islamic State, noting that the president is "trying to kill them."

Over the past two years Obama has organised a broad coalition of countries and launched more than 10,000 U.S. airstrikes to defeat IS.

"I don't care," the billionaire businessman replied. "He was the founder. The way he got out of Iraq, that was the founding of ISIS, OK?"

In a later speech to home builders in Miami today, Trump said his Democratic opponent, Hillary Clinton, would be given "the most valuable player award" by IS.

"Her only competition is Barack Obama," he said. He later added of Clinton, "Oh boy, is ISIS hoping for her."

Clinton's campaign accused Trump of "trash-talking" the US while failing to present any serious counter-terrorism plans of his own.

Jake Sullivan, Clinton's top policy aide, called Trump's accusation a "false claim" and drew a connection to Russian President Vladimir Putin.

"Once again, he's echoing the talking points of Putin and our adversaries to attack American leaders and American interests," Sullivan said.

Dozens of frustrated Republicans, meanwhile, gathered signatures today for a letter to Republican National Committee Chairman Reince Priebus that urges the party chief to stop helping Trump and instead focus GOP resources on protecting vulnerable Senate and House candidates.

A draft of the letter, obtained by The Associated Press, warns that Trump's "divisiveness, recklessness, incompetence, and record-breaking unpopularity risk turning this election into a Democratic landslide."

At least 70 Republicans have signed the letter so far, according to Republican operative Andrew Weinstein, who said it included five former members of Congress and 16 former RNC staffers.