Wary of Donald Trump, G.O.P. Leaders Are Caught in a Standoff

Two of the most potent financial networks in Republican politics, that of the hedge fund billionaire Paul Singer and another led by the industrialists Charles G. and David H. Koch, have each had preliminary conversations about beginning an anti-Trump campaign, according to strategists involved. But Mr. Trump has already mocked Mr. Singer and the Kochs, and officials linked to them said they were reluctant to incur more ferocious counterattacks.