Mitt Romney is moving quickly to reassemble his national political network, spending the weekend and Monday calling former aides, donors and other supporters — as well as onetime foes such as Newt Gingrich. Romney’s message was that he is serious about making a 2016 presidential bid. He told one senior Republican he “almost certainly will” run in what would be his third campaign for the White House, this person said. His aggressive outreach over the past three days indicates that Romney’s declaration of interest to a group of donors in New York Friday was more than the release of a...