Washington (AFP) - The White House angrily challenged Republicans to denounce their party's presidential frontrunner Donald Trump Tuesday, claiming his "toxic" plan to ban Muslims from entering the country should disqualify him from office.

Painting Trump as a "carnival barker" with "fake hair" whose campaign belonged in the "dustbin of history," White House spokesman Josh Earnest said Trump's plan to refuse even American-born Muslims entry to the United States were patently unconstitutional.

"What Donald Trump said yesterday disqualifies him from serving as president," said Earnest sharply, describing the 69-year-old's comments variously as "offensive" and "toxic."

The unusually strident language from the White House podium reflects concern about the impact of Trump's comments in the wake of a mass shooting that killed 14 in California that is being blamed on Islamic extremists.

But it also suggests that the White House spies a political opportunity ahead of the 2016 election.

Earnest was quick to pounce on prominent Republicans who condemned Trump's remarks -- including rival presidential contenders Marco Rubio, John Kasich, Chris Christie and Jeb Bush -- saying they would still support him if he were the party nominee.

The "Grand Old Party" has long held fast to late president Ronald Reagan's so-called 11th commandment: "Thou shalt not speak ill of any fellow Republican."

Earnest dared them to break that rule and challenge Trump, or risk being tarred with the same brush.

"What he said is disqualifying and any Republican who's too fearful of the Republican base to admit it, has no business serving as president either," he said.

That poses a dilemma for Republicans who may have little love for Trump: refuse to withdraw support and risk being branded a bigot, or withdraw support with the political risks that entails.

- Staying power -

The politically savvy real estate mogul took to Facebook Friday to make sure every Republican knows the danger of choosing the latter.

Story continues

"A new poll indicates that 68 percent of my supporters would vote for me if I departed the GOP and ran as an independent," he said.

Trump currently leads Republican presidential polls by double digits.

According to a USA Today/Suffolk survey published Tuesday he is supported by 27 percent of Republican likely voters.

His nearest rival Senator Ted Cruz stands on 17 percent, with Senator Marco Rubio on 16.

Analysts suggested Trump's latest provocation was a calculated ploy to whip up support before the first primary nomination votes in Iowa and New Hampshire in February.

Trump has already galvanized core conservative voters fearful of undocumented workers taking US jobs with his oft-repeated pledge to build a wall along the Mexican border.

American University professor of government Jennifer Lawless said it was unlikely Trump would be able to win the nomination "entirely on immigration."

"But if you can link immigration to terrorism and foreign policy and national security, then you have the potential to cast a much wider net."

Trump has defied the pundits with his staying power, remaining the frontrunner with just two months until Iowa becomes the first state to vote on the nomination.

Spending very little of his fabled billions on advertising, Trump's campaign has been defined by outlandish remarks on television and social media that spur yet further media attention.

"The question now is about the rest of the Republican party and whether or not they're going to be dragged into the dustbin of history with him," said the White House's Earnest.

"And right now, the current trajectory is not very good."