Rep. Nancy Pelosi (D-Calif.) has only lost one major vote since becoming Speaker.

And with a roll call expected on a landmark healthcare bill as early as next week, she is facing one of her toughest tests yet: bringing together a caucus split between factions engaged in open warfare.

Pelosi's ability to unite Democrats and get the tough bills passed derives from her powers of persuasion and careful vote counting. And part of counting votes is knowing whom you can count on in a pinch.

Here are some of the key Democrats Pelosi is likely to turn to as the voting on healthcare reform comes down to the wire, along with two hard-to-get votes.

Rep. Dennis Cardoza (Calif.): Cardoza is Pelosi's ambassador to the Blue Dog...