• President Trump is moving toward breaching an established constraint on executive power: that the White House does not make decisions about individual law enforcement investigations.

In an extraordinary meeting, he summoned the F.B.I. director, Christopher Wray, center left, and the deputy attorney general, Rod Rosenstein, center right, to the White House to apply pressure on the Russia inquiry.

It’s part of an increasingly aggressive strategy to contain the threat and undercut the credibility of the escalating investigations targeting the president and his associates.

Mr. Rosenstein has agreed to meet increasingly onerous demands from Mr. Trump and his allies, and legal scholars and former law enforcement officials worry that such moves could allow the Justice Department to be used as a cudgel to attack presidents’ political enemies.

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