LONDON — In nearly a millennium of history, the Palace of Westminster has played host to kings and queens, endured Nazi bombing raids and showed the world how a people could govern themselves through representative democracy.

But it has never seen a day like the one expected Monday, when the building will echo with a parliamentary debate over whether to ban from Britain the leading Republican contender for U.S. president.

It will be a strange moment for politics on both sides of the Atlantic. Normally, British officials avoid getting involved in U.S. politics – and vice versa. The Anglo-American alliance, a bedrock of Western security, is supposed to transcend politics.

Donald Trump’s emergence as Republican front-runner, however, is putting that notion to the test. Brits have watched his rise with a mixture of bemusement, alarm and indignation – the latter coming after he alleged that certain areas of London were off-limits to police because of rampant Islamic radicalization.

The debate was triggered when more than a half-million people signed an online petition arguing that Trump should be outlawed from visiting Britain because of his call last month to ban Muslims from entering the United States. Trump’s proposal, petitioners said, amounted to “hate speech.”

For three hours Monday, members of Parliament will have a chance to say whether they agree. But while Trump’s words have been widely condemned in Britain – from all sides of the political spectrum – there is little chance he will be banned. Instead, he may well find himself invited for a visit.

“I’d offer myself as a guide to take him around town,” said Paul Flynn, a member of Parliament from the center-left Labour Party. “I’d be delighted if he took me up on it.”

Flynn has been designated to argue on behalf of the petitioners who want Trump banned – and Flynn said he has sympathy for their cause. Trump’s remarks on Muslims, Mexicans, women and the disabled, Flynn said, “are outrageous.” But Flynn said he will ultimately argue against a ban.

“The last thing we want to do is assist him by awarding him a garland of victimhood,” he said.

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