Just as Democrats were starting to count him out, Joe Biden sent a clear signal through his political team that not only might he enter the presidential race soon, he has a strategy prepared that he thinks could win.

After months of growing calls for him to run, the vice president’s tide began turning this week after the first Democratic debate, which softened concerns about front-runner Hillary Rodham Clinton while obscuring any obvious rationale for Biden to run. But in a letter to former Biden staffers late Thursday, one of Biden’s closest advisers traced the contours of the argument Biden would make, and suggested a decision to run could be imminent.