Republicans have been vocal about their hang-ups with the bill throughout the week, but more recently some Democrats, including Sen. Tom Harkin of Iowa, Sen. Ron Wyden of Oregon and Sen. Dianne Feinstein of California, were also wavering.
To get the 60 votes necessary to end debate and vote for passage, the bill likely would have needed the support of at least 10 Republicans, probably more.
Missouri's Sen. Kit Bond, one of the few Republicans who had supported a bailout, said the version passed in the House "fails" to force needed reforms on the auto companies.
"While I am fighting to save Missouri auto jobs, Congress is just putting off the inevitable unless we force the companies to reform fundamentally, which this latest plan fails to do and is why I am offering changes to make it work," Bond said in a statement.
Sen. David Vitter, R-La., condemned the White House's approach to provide money before the carmakers prove they have workable plans for restructuring.
Others object to the idea that a government-appointed "car czar" would know how to fix the industry and say the money will simply be wasted with no real changes being made.
"Americans are not stupid," said Sen. Jim Demint, R-S.C. "They know this bailout is only a temporary solution."
"The public doesn't like it," McConnell said. "And in our line of work, that's important."
As Republicans lashed out at specific elements of the package, the White House came out in its defense Wednesday, saying in a statement that the legislation developed with congressional Democrats to rescue automakers is an "effective and responsible approach" that will "ensure the necessary restructuring occurs."
Congressional Democrats drafted the latest text of the measure Wednesday after coming to an agreement with the White House on the language.
"This gets us to the 20-yard line, but getting over the goal line will take a major effort," said Sen. Carl Levin, D-Mich., Tuesday night. "We will need the personal involvement of President Bush and President-elect Obama."
For the measure to pass in the House, Pelosi caved on several major points. According to her aides, she now feels the House bill is a "take it or leave it" proposition to the Senate.
The bill, first sent to the White House Monday, would provide Chrysler and General Motors with a short-term infusion in low-interest loans to stay afloat in the months ahead. It also would call on Bush to select one or more people within the executive branch to authorize, disperse and oversee a loan for the auto industry.
The car czar would have the power to reshape the industry and negotiate deals among auto companies, unions, creditors and suppliers. The designee also could force car companies into Chapter 11 bankruptcy if they don't have a viability plan by March 31.
"They either have a long-term plan that's viable, or we get our money back," White House deputy chief of staff for policy Joel Kaplan, who is leading White House negotiations on the bailout, said today. "And if we call our money back, which is required under this bill, then those firms are not going to be able to survive."
General Motors, Chrysler and Ford have repeatedly made their case to lawmakers and U.S. taxpayers to explain why they need a loan. GM CEO Rick Wagoner told lawmakers last week that, without an infusion of $4 billion in taxpayer loans before the end of the year, the company would go bankrupt.
Negotiators have decided that Ford, not in immediate need of a loan, will not receive funding at this point.
ABC News' Kirit Radia, Rachel Martin and Dean Norland contributed to this report.
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