LONDON — In almost every way, British Prime Minister Keir Starmer will walk into the White House on Thursday as an alien in President Donald Trump’s MAGA universe: a former human rights lawyer, a onetime top prosecutor and, after vanquishing Conservatives in elections last summer, the United Kingdom’s most liberal leader in more than a decade.

The White House said on Tuesday it would decide which media organizations participate in the press pool that covers the president, wresting control away from the group of journalists that has done so for decades.

The White House said Tuesday that its officials “will determine” which news outlets can regularly cover President Donald Trump up close — a sharp break from a century of tradition in which a pool of independently chosen news organizations go where the chief executive does and hold him accountable on behalf of regular Americans.