What Mr Trump’s saying about how to handle this war is empowering the enemy,” said Senator Lindsey Graham, one of a dozen candidates trailing Trump in the race for the Republican presidential nomination.

Mr Graham said that Isis “loves Donald Trump because he is giving them an opportunity to bring people their way.”

This is a damning accusation that would seem to run against the views of millions of American voters.

And this was before Mr Trump sparked near-universal opprobrium with his call to ban Muslims from entering the United States.

A new New York Times/CBS News poll found that Republicans have more confidence in Mr Trump to address terrorism than any other candidate.

Seven in 10 voters said he was well equipped on the issue.

The poll was conducted largely before Mr Trump’s latest comments, but straight after a mass murder in California by husband-and-wife killers who authorities have described as Isis sympathisers.

Even before his suggestion of a Muslim travel ban, Mr Trump has been outspoken, expressing support for the creation of a government registry of Muslims in America, accusing the Obama administration of planning to flood the country with Syrian refugees, and calling for the surveillance of mosques and potentially the closure of some of them.

DANGEROUS TERRAIN

He argues that the US has to consider stronger new measures in order to protect itself from terrorism.

He also seems to question the loyalty of American Muslims who have never broken the law or posed any kind of threat.

Mr Trump told his supporters that he saw thousands of Muslims celebrating in New Jersey during the World Trade Centre attacks of September 11, 2001, although there is no evidence of such an event and a number of New Jersey officials, including the governor, have denied that this ever happened.

“Trump is trafficking in very dangerous and populist rhetoric: essentially if we build a wall, or keep them out or put them in a national registry, then ISIS will go away,” said Mr Michael Weiss, a CNN analyst who is co-author of Isis: Inside the Army of Terror. 

“Making this case, that it’s the West versus Islam, is what Isis is doing. So in a sense, Trump is underwriting their propaganda for them.”    

Republicans are split in their reaction to Mr Trump’s remarks. Most of the other Republican presidential candidates have denounced them.