WASHINGTON - The White House on Tuesday challenged Republicans to denounce their party’s presidential frontrunner Donald Trump, claiming his proposal to ban Muslims from travelling to the US should disqualify him from being commander-in-chief.

Painting Trump as a “carnival barker” with “fake hair” whose campaign has a “dustbin of history” quality, White House spokesman Josh Earnest said Trump’s proposals were unconstitutional.

“What Donald Trump said yesterday disqualifies him from serving as president,” said Earnest, describing his comments variously as “offensive” and “toxic.”

The unusually strident language from the White House reflects a concern about the impact of Trump’s comments on US Muslims and the fight against the Islamic State group, but it also indicates the White House spies a political opportunity ahead of the 2016 election.

Earnest was quick to pounce on leading Republicans who condemned Trump’s remarks, but said they would still support him if he were the party nominee.

“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.

The condemnation of Trump’s exclusionary initiative, which began within moments of its unveiling Monday, gathered strength as more prominent Republicans, among them House Speaker Paul Ryan, weighed in. “This is not conservatism. What was proposed yesterday… is not what this party stands for,” the Wisconsin Republican told reporters on Capitol Hill. “And more importantly, it’s not what this country stands for.”

Other members of the Republican establishment weighed in as well.

In tweets and public statements, the party heads in Iowa, New Hampshire and South Carolina — three of the earliest voting states — took issue with Trump’s call to bar members of the Islamic faith from entering the United States for an indefinite time “until our country’s representatives can figure out what is going on.”

“As a conservative who truly cares about religious liberty, Donald Trump’s bad idea and rhetoric send a shiver down my spine,” Matt Moore, chairman of the South Carolina Republican Party, wrote on Twitter. “American exceptionalism means always defending our inalienable rights, not attacking them when it’s politically convenient.”

Jennifer Horn, head of the New Hampshire, said Trump’s proposal was “un-American” and “un-Republican.” Jeff Kaufman, chairman of the Iowa Republicans Party, said on Twitter, “We don’t make ourselves safer by betraying bedrock constitutional values.”