Robin Carnahan, the challenger of the bunch.

Two Senate Democrats have joined a challenger for an open seat in forming a joint fundraising committee for 2010 with the help of the Democratic Senatorial Campaign Committee.

All three are in competitive races in Senate Victory 2010 fund created May 28. The fund will benefit Sens. Christopher J. Dodd of Connecticut and Michael Bennet of Colorado, and Missouri’s Secretary of State, Robin Carnahan , who seeks the seat of retiring Republican Sen. Christopher S. Bond .  

Such joint fundraising committees allow candidates to hold single events with contributors writing a single check for multiple candidates, who then split the proceeds with the national committee. But they also create accounting headaches because contribution limits from individuals still apply. For example, if a contributor has already given the maximum $2,400 per election to Dodd, any contribution to the joint committee must be divided among the others.