As the Senate heads toward a cloture vote on President Obama’s $447 billion jobs bill tonight, Republicans said Democrats have “designed” the bill to fail.

“They have designed their own bill to fail in the hopes that anyone who votes against it will look bad for opposing a bill they have mistakenly referred to as a jobs bill,” Senate Minority Leader Mitch McConnell, R-Ky., said on the Senate floor this afternoon.

And the bill does seem almost certain to fail in the Senate tonight.

Tonight’s cloture vote is  merely a means to open debate on the jobs bill, which requires 60 votes to pass. Democrats  need Republican support for the bill to pass, which they do not have.  Not even  all 53 Democrats are expected to vote for the bill.

President Obama  said as recently as today that any senators who vote  ”no” on the bill will have to explain their reasons. Today McConnell tried to flip that around a bit.

“Everyone who votes for this second stimulus will have to answer a simple but important question: Why on earth would you support an approach that we already know will not work?” McConnell asked. “The truth of the matter is most Democrats know as well as I do that passing another stimulus and tax hike has allowed the idea, which is why the Democrats are having such a hard time convincing their colleagues to vote for it.”

All 47 Republicans are expected to vote against the jobs bill.

The key to this vote will be watching the Democratic defectors, especially those moderates up for re-election next year, such as Sens. Ben Nelson, D-Neb., and Joe Manchin, D-W.Va., whose votes will matter in their election messaging. Both Manchin and Nelson will likely vote no on the bill, dwindling the opportunity for a strong Democratic showing tonight.

A Democratic vote against the president’s bill would be a major blow to the White House, especially if there are more than a few no’s and if the bill fails to get even  51 votes. As of now, it looks as if the Democrats could get  fewer than 50 votes for the Democratic bill.

Sen. Jon Tester, D-Mont., has said that he’d oppose the ultimate vote on the jobs bill but has not indicated how he’ll vote on tonight’s procedural but symbolic vote – so his support tonight is not assured.

Sen. Jeanne Shaheen, D-N.H., supports the bill but is scheduled to be in Boston this evening to receive the .New Englander of the Year award. She has told the Democratic leadership that she would return to Washington tonight if her vote is needed for passage.

McConnell said that Republicans “welcome the opportunity” to vote tonight on the jobs bill, because it means they can move forward and start working on a bipartisan approach.

“If voting against another stimulus is the only way we can get Democrats in Washington to finally abandon this failed approach to job creation, then so be it,” McConnell said. “How about we get this vote the Democrats already know won’t pass behind us so we can focus on real job-creating legislation that we actually know is worthy of passing with bipartisan support.”

Senate Majority Leader Harry Reid, D-Nev., who added the Democratic revision of a 5.6 percent  surtax on millionaires to Obama’s jobs bill to gain more Democratic votes  cast tonight’s vote as a sign — and comparison — of who each party puts first.

“Today we’ll see whether the Republicans have gotten the message or if they still put the wants of millionaires and billionaires ahead of the needs of seniors and middle-class families,” Reid said. “I guess Republicans think if the economy improves it might help President Obama. They root for the economy to fail and oppose every effort to improve it.”

UPDATE at 17:49 ET:

In an effort to pick up another Democratic vote, the Democratic leaders intend to hold the vote open tonight for Senator Jeanne Shaheen, D-NH,. who was scheduled to be in Boston this evening to receive the “New Englander of the Year,” award. Senator Shaheen’s office say she will be returning to the Capitol late tonight to vote.  Shaheen is not scheduled to land in DC until about 8:45 pm which means that the vote on the jobs bill will be held open until at least then.

And Sen. Jim Webb, D-VA., has clarified his statement on the Senate floor. He will vote for the bill tonight, but will not support final passage of the bill in its current form (which, if the bill is voted down tonight will never happen.) Webb’s statement is below:

“Out of respect for the principles of free and open debate, I will be voting to proceed to debate on the American Jobs Act.  However, I cannot support final passage of the bill in its current form,” Webb says in a paper statement, “I again emphasize my belief that rather than increasing taxes on wages or ordinary income, the bill should be paid for by other means such as raising the capital gains rate or ending costly subsidies and tax loopholes.”