Nelson's support for the bill is considered crucial for its passage since most Republicans oppose the measure. Despite having reservations about the bill, Nelson did not say whether he would support the legislation.
Senate Majority Leader Harry Reid (D-Nev.) hopes to file cloture on the new bill this evening, setting up a procedural vote on the measure by Friday, at the latest.
Sources say Reid has been courting Republican Sens. Susan Collins (Maine) and Scott Brown (Mass.) for the two conservative votes needed to advance the bill if Nelson chooses to oppose the measure.
Brown told The Hill that the bill has to be fully paid for to earn his vote.
"They've got to pay for it," he said. "The whole thing."
Collins struck a more positive note about changes to the bill but stopped short of saying she supports the bill.
"It appears that real progress has been made today," she said, adding, "[But] I need to look at the tax side of the package."
Collins wants to be sure that new tax increases have not been included in the bill to pay for more of its measures.
"If they've offset the cost, I want to make sure they've offset it with spending and with obligated stimulus money and not through a bunch of new tax increases," she said.
Reid is also looking for support from Sen. Joe Lieberman (I-Conn.). The senator refused to speak with reporters today about changes made to the bill.