I talked to a couple of Romney people about the decision today. They say that Mitt strongly believed that he could win the nomination, but feared that he wouldn’t be best-suited to win the general election, especially after getting bloodied in a primary. And if he didn’t win the nomination, he would only have played a role in bloodying the eventual nominee (a process he’s familiar with, having suffered through it in 2012). They say he thought enough donors would have been there for him, even if he inevitably lost some to Jeb, and that even until the very end he was torn about whether to go again or not. In the last few weeks, he wanted to take a good, long look at the race and see if there was any real support out there, beyond kind comments at airports and the early polls. He felt that there was, and there was a period the last few weeks when the people close to him were convinced he would run. But he knew the window to get in was closing, so he had to make the decision soon, hence the announcement today. One friend and advisor compared it to his decision to get out in 2008, when he could have hung on longer against McCain, but decided it wouldn’t serve the party’s interests. He will stay involved in the process, and could even endorse, but not anytime soon.