Bernie Sanders is doing his share, but Massachusetts Sen. Elizabeth Warren has thrown herself even more aggressively into Senate Democrats’ debate over their future direction. The Michigan trip is notable because Warren first supported Mallory McMorrow, who later dropped out. Senate Democrats have three contested primaries left on the calendar — and Warren is involved in all of them. In addition, Warren has endorsed Rep. Chris Pappas, D-N.H., who is breezing toward the general election. “In Democratic primaries, we should give candidates themselves a chance to build their own campaigns,” Warren added.