Rep. Michele Bachmann (R-Minn.), who's weighing a run for president in 2012, will share a stage later this month with South Carolina Gov. Nikki Haley (R), whose endorsement will be one of the most coveted in next year's GOP primary.

Bachmann is set to speak at a rally organized by the Columbia Tea Party on April 18, capping a swing through the state slated to begin on April 15, her camp confirmed. Haley is among the rally's headliners and has already declared her intention to endorse a candidate before the state's GOP primary next year.

Bachmann has made trips to the early states of Iowa and New Hampshire in recent weeks and is expected to form a presidential exploratory committee by early summer. 

During Haley's 2010 race for governor, she was endorsed by a litany of rumored presidential hopefuls, including former Alaska Gov. Sarah Palin, former Massachusetts Gov. Mitt Romney, former House Speaker Newt Gingrich (Ga.) and former Minnesota Gov. Tim Pawlenty.

In the 2008 presidential race, Haley was a Romney backer.