In a speech on the floor of the Senate Tuesday, Manchin declared his intention to vote against the Democratic version and blasted President Obama for a failure to lead on the budget. 

"Why are we doing all this when the most powerful person in these negotiations — our president  — has failed to lead this debate or offer a serious proposal for spending and cuts that he would be willing to fight for?" Manchin said Tuesday.

Both Manchin and McCaskill are among the Senate Democrats caught in the middle in the spending debate and are under continuous attack from Republicans who sense vulnerability in 2012. Both are top GOP targets.

The National Republican Senatorial Committee quickly went after McCaskill and eight other Democrats whose seats are up in 2012 for voting against the House GOP plan. 

“If every Missouri family and small business took the same approach to spending and debt that Claire McCaskillClaire Conner McCaskillTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand Feds allow campaigns to accept discounted cybersecurity services GOP frets over nightmare scenario for Senate primaries MORE takes with spending their tax dollars, every single one of them would be bankrupt and destitute," NRSC spokesman Chris Bond said after Wednesday's vote.

Another Republican target in 2012 -- Sen. Jon TesterJonathan (Jon) TesterTrump nominees meet fiercest opposition from Warren, Sanders, Gillibrand The Hill's 12:30 Report: Pelosi looks to squash fight with progressives Democratic senators want candidates to take Swalwell's hint and drop out MORE (Mont.) voted in favor of the Senate Democratic plan to cut $4.7 billion Wednesday.

Three Senate Republicans also voted against the House plan Wednesday, arguing the cuts aren't deep enough. Sens. Rand PaulRandal (Rand) Howard PaulFirst responder calls senators blocking 9/11 victim funding 'a--holes' The Hill's Morning Report - Trump seizes House impeachment vote to rally GOP Jon Stewart rips into Rand Paul after he blocks 9/11 victim compensation fund: 'An abomination' MORE (Ky.), Mike LeeMichael (Mike) Shumway LeeFirst responder calls senators blocking 9/11 victim funding 'a--holes' Jon Stewart rips into Rand Paul after he blocks 9/11 victim compensation fund: 'An abomination' Senate approves long-delayed tax treaties in win for business MORE (Utah) and Jim DeMint (S.C.) all voted "no." 

Along with the five Democrats up for reelection next year, another six Senators who caucus with Democrats voted against the Democratic measure Wednesday. Sens. Kay Hagen (N.C.), Bernie SandersBernie Sanders2020 Democrats react to 'send her back' chants at Trump rally Cardi B posts message of support for Ilhan Omar #IStandWithIlhan trends after crowd at Trump rally chants 'send her back' MORE (Vt.), Jim Webb (Va.), Michael BennetMichael Farrand BennetNew CDC overdose estimates are nothing to celebrate Bullock makes CNN debate stage Sanders draws line as 2020 health care battle heats up MORE (Colo.), Carl LevinCarl Milton LevinListen, learn and lead: Congressional newcomers should leave the extremist tactics at home House Democrats poised to set a dangerous precedent with president’s tax returns The Hill's 12:30 Report — Sponsored by Delta Air Lines — White House to 'temporarily reinstate' Acosta's press pass after judge issues order | Graham to take over Judiciary panel | Hand recount for Florida Senate race MORE (Mich.) and Mark UdallMark Emery UdallDemocrats hope some presidential candidates drop out — and run for Senate  Denver Post editorial board says Gardner endorsement was 'mistake' Gardner gets latest Democratic challenge from former state senator MORE (Colo.) also voted "no." 

-Updated at 4:32 p.m.