Sen. Scott Brown, the Massachusetts Republican who replaced the late Ted Kennedy in the Senate, plans to formally begin his reelection campaign at a rally on Jan. 19.

The Massachusetts Senate race will be a closely watched contest not only because Brown is a Republican in a liberal state but because of the attention given to Elizabeth Warren, his opponent who left her job as an adviser to President Obama to run in the race.

Brown sent his supporters an invitation to his "campaign kickoff" in Worcester, Mass., today, claiming that his reelection bid will be "another uphill battle."

"Representing Massachusetts in the Senate has been the honor of my life," the invitation says. "But after only two short years, there is still much work to do to fix a broken Washington, get our economy moving again, and put our nation back on the right track."

The event will happen exactly two years after Brown defeated Martha Coakley in the Massachusetts special election for Kennedy's Senate seat.