Washington— 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. The first Democratic debate 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 could be imminent. Former Sen. Ted Kaufman said if Biden runs, it will be because of his "burning conviction" to restore opportunity to the middle class.