Former vice presidential candidate Sarah Palin and Rep. Michele Bachmann (R-MN) both appear poised to launch formal presidential campaigns, offering the prospect of two candidates who are ascendant party celebrities with the power to electrify voters.

But Palin and Bachman could ultimately undercut each other by offering similar messages that would split an already fractured base. They would be jostling with a half dozen other candidates, none of whom garnered as much as 20 percent of the vote in a recent Gallup poll.

Bachmann has fueled speculation that she is on the verge of announcing with a trip to Iowa. Palin has begun reconstituting her staff and making plans to increase her public appearances. Meanwhile, the Republican field has taken shape in recent days, with high-profile candidates such as Indiana governor Mitch Daniels and former Minnesota governor Tim Pawlenty official declaring whether or not they will run.

Both Palin and Bachmann have risen to prominence in recent years through their vocal denunciations of the Obama administration, particularly the new healthcare law, and their calls to pare back spending. Their populist messages resonated with the Tea Party, and in the 2010 midterm elections Palin established herself as a party kingmaker capable of helping Republican candidates she anointed win the party's nomination. Bachmann has also become a Tea Party folk hero, choosing to deliver a response to Obama's State of the Union address on behalf of the Tea Party.

Still, Palin's national recognition and acumen on the campaign trail gives her a clear advantage in a matchup with Bachmann, longtime Republican campaign adviser Steve Lombardo said.

There's little doubt that both Palin and Bachmann appeal to a similar voter segment, but I do think that at this point in time Palin's voter appeal is greater, Lombardo said. Within certain elements with the Republican party as well as the Tea Party Palin is a rock star. I think Bachmann is trying to become one but she's not there yet.

The attempt to model themselves as renegades may have cost Bachmann and Palin some political points. In 2010 Palin endorsed candidates outside of the mainstream, including Sharron Angle in Nevada and Christine O'Donnell in Delaware, who were nominated but espoused radical views that helped to swing highly contested races to Democrats. Bachmann's State of the Union response angered some Republicans who saw her as trying to upstage the official response, offered by Paul Ryan (R-WI).

But Lombardo said that their influence has also waned without elections to galvanize voters, and suggested that the Tea Party message of cutting spending still has sufficiently broad appeal that it will no doubt be adopted by most of the candidates.

There's probably been some erosion in their popularity and their sway over the Republican party over the last 12 months just because Tea party has diminished a little bit in terms of the role it's playing in the Republican party, Lombardo said. That's going to start change towards the end of this year.