Late Monday afternoon, Republican electors in Texas vaulted Mr. Trump past the 270 mark, giving him 36 votes, with one each for Gov. John Kasich of Ohio and Ron Paul. Presidential electors — and particularly Republican electors, who are bound by tradition and often state law to support Mr. Trump — were inundated with phone calls, emails and even threats demanding that they vote for someone else. Leaders of groups that were lobbying the electors had privately believed they had a chance to persuade enough Republican electors to defect, denying him an Electoral College majority and throwing the election to the House of Representatives. But by late Monday, only a handful of electors had broken ranks.