Sen. Claire McCaskill said Wednesday that she'll vote against her party's deficit reduction plan when it comes up for a vote today.

McCaskill, the centrist Missouri Democrat who faces a tough 2012 reelection battle, said she'll vote for neither the Republican nor the Democratic plan today.

The Republican plan, which passed the House and would cut $57 billion the rest of this fiscal year, "represents the wrong priorities," McCaskill said in a conference call with Missouri reporters.

"On the other hand, I believe the Democratic proposal also falls short, because the cuts are not substantial enough," McCaskill added. "They represent another $6.5 on top of the $4 billion we've already cut, and I think we need to do more [...] the Democratic proposal falls short."

McCaskill is the second Democrat to formally declare her opposition to the Democratic-favored spending bill.

Sen. Joe Manchin (D-W.Va.) also said the Democratic proposal didn't cut enough in a Senate floor speech on Tuesday taking President Obama to task on the issue.

Another centrist, Sen. Ben Nelson (D-Neb.) said Wednesday he will vote against the Republican and Democratic spending bills. 

-- This post was updated at 12:45 p.m.