Updated: 2:45 p.m.

Senate Democrats are turning a debate on a bill giving tax breaks to companies that bring jobs to the U.S. from abroad as a proxy fight over presumptive Republican presidential nominee Mitt Romney and his time as head of Bain Capital.

At a press conference today, Senate Majority Leader Harry Reid (D-Nev.) said it was likely that Senate Republicans would filibuster the measure, not on substance but for political reasons.

“Its fairly easy to see why Republicans are blocking our bill to stop outsourcing. They are obviously defending their presidential nominee, who of course made a fortune by shipping jobs overseas,” Reid said.

The Senate’s 56-42 procedural vote this afternoon fell short of the 60 needed to proceed.

Democrats charge that Romney headed Bain Capital when it invested in businesses that shipped jobs overseas.

“So it’s no wonder Republicans are afraid of a debate over shipping jobs overseas,” Reid said.

Senate Minority Leader Mitch McConnell (R-Ky.) has said that he is open to a debate but wants Republicans to get votes on their amendments to the bill.

Reid and McConnell have been increasingly butting heads on the issue, as Democrats want to keep the amendments related to the topic under discussion.

“A number of my Members are asking in connection with voting to proceed to the bill whether the bill will be open for amendments,” McConnell said to Reid on the floor.

Reid responded that the only amendments he had seen were not related to curbing outsourcing of jobs and then said he was “very doubtful” of the prospect for allowing amendments.

McConnell then signaled Republicans would not be inclined to vote in favor of the bill without being given an opportunity to help craft it.

“Apparently, the bill will not be open for amendment and we’ll take that into consideration in deciding whether or not to support cloture on the motion to proceed,” McConnell said.

Debate over taxes is expected to continue into next week when Senate Democrats will seek to hold a vote on a bill to extend the 2001 and 2003 tax cuts for households making less than $250,000, a position that President Barack Obama has been pushing in a tour through swing states this week.

Republicans oppose the bill because they believe it will hurt hiring at small businesses and want a vote on their proposal to extend all the tax cuts for one year.

Reid also underscored that allowing the tax cuts to expire and automatic spending cuts to hit next year is not Democrats’ preferred position, but he said it is something they are willing to do given that all efforts to reach a bipartisan deal on deficit reduction have failed because of Republican opposition to raising taxes.

“All that anyone asked on the Democratic side is just a little bit of help with revenue,” Reid said. “There doesn’t have to be a fiscal cliff. We could do it before we leave here in August, we could do it when we come back in September, all they have to do is give some revenue and we can do this. The fiscal cliff does not have to be there. It’s all up to the Republicans.”

Niels Lesniewski contributed to this report.