WASHINGTON — President Donald Trump and his top advisers threatened on Monday to unleash the power of the federal government to punish what they alleged was a left-wing network that funds and incites violence, seizing on Charlie Kirk’s killing to make broad and unsubstantiated claims about their political opponents.

Investigators were still working to identify a motive in the death of Kirk, a prominent conservative activist who was shot last week in Utah. The Republican governor of Utah, Spencer Cox, has said that the suspect had a “leftist ideology” and that he acted alone.

But Trump and his top allies suggested that the suspect was part of a coordinated movement that was fomenting violence against conservatives, without presenting evidence that such a network existed. America has seen

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