President Trump on Tuesday turned up the pressure on recalcitrant Republicans to support a sweeping bill to overhaul the health care system, threatening wavering lawmakers in his party with political payback if they failed to get behind a measure that has become an early test of his negotiating power. In a series of meetings and phone calls at the White House and on Capitol Hill, Mr. Trump, Vice President Mike Pence and Republican congressional leaders haggled with holdouts over details as they struggled to assemble a majority to support a bill that would repeal and replace the Affordable Care Act. The legislation is scheduled for a floor vote on Thursday in the House. But at a private meeting with House Republicans at the Capitol, the president also delivered a blunt warning that many of those present would lose their seats in next years midterm congressional elections if the effort failed. I’m going to come after you, Mr. Trump told Representative Mark Meadows, Republican of North Carolina, a prime holdout and the chairman of the conservative Freedom Caucus, a hotbed of concern about the legislation, according to several people in the room who described his comments on condition of anonymity because the session was private. I believe Mark and his group will come along, because honestly, a loss is not acceptable, folks. It is not clear whether Mr. Trump would be able to exact a political price from Republicans who opposed the measure; conservative groups including the Club for Growth and Heritage Action for America were lining up against the legislation and pressuring lawmakers to oppose it, raising questions about whether it would be possible to mount a successful primary challenge to defectors. And some Republicans said the political peril would be greater if they supported the health care bill, which they said failed to achieve their goals or those of their constituents.