President Obama will head to California next month to campaign for Sen. Barbara Boxer (D-Calif.)

The Boxer campaign announced today that Obama will attend a joint fundraiser for the Democratic National Committee and Boxer's re-election campaign in April.

Once thought to be a lock for re-election, Boxer is now facing the prospect of a tough campaign in what's shaping up to be a Republican-friendly election cycle.

Three Republicans are competing to take on Boxer: former HP CEO Carly Fiorina, former Rep. Tom Campbell (Calif.), and Assemblyman Chuck DeVore.