Fearing a political backlash against Democrats, Senate Majority Leader Harry Reid (D-Nev.) has told the White House that it must serve up support from Republican presidential nominee Sen. John McCain (Ariz.) if it hopes to ensure bipartisan backing for a massive economic bailout package by week’s end.

Reid made his position clear to Treasury Secretary Henry Paulson on Monday night, as well as to his Democratic caucus, which shares many of the GOP’s concerns that the $700 billion bailout has been drafted too hastily and is a risky remedy for an economy on the brink of crisis. Reid, according to Democratic Senate sources, also wants assurances from Senate Republican leaders that an evenly divided, bipartisan group of Senators will pass any legislative fix so his party isn’t left with the burden of doing an unpopular White House’s bidding — again.

“If the administration wants us, we are going to have to go hand in hand or at the end of the day, it’s not going to happen,” Sen. Bob Menendez (D-N.J.) said.

Democratic leaders have privately been eyeing a strategy — to be worked out with the White House and GOP Senate leaders — that would call for an equal number of Senators in each party supporting the final bailout plan. Talks have included splits of 30 Democrats and 30 Republicans or higher to ensure neither party is labeled with being responsible for the costly package.

“Harry Reid would like Republican Senate support, whatever remedy we come up with,” Sen. Mark Pryor (D-Ark.) said. “Right now, there’s significant opposition on the Republican side. Democrats have serious concerns about Paulson’s proposal, but we are willing to work with the Treasury Department and the Fed to come up with the right solution.”

Sen. Bob Casey (D-Pa.) agreed, saying, “we need help from both parties” if a bill is to be completed in the coming days. Casey, who sits on the Senate Banking, Housing and Urban Affairs Committee, said the administration needs to do more to get Republicans invested in a solution.

“I think if you look at the Republican side, at the McCain campaign and the leadership, I’m not convinced they are working to get their side to the table,” Casey said. “But the week is young.”

McCain holds the key to such a bipartisan vote, according to Reid, because Republicans are likely to defer to his position on a bill that holds political peril. McCain on Tuesday night joined Democratic presidential nominee Sen. Barack Obama (Ill.) in lending qualified support for the $700 billion package, but it remains unclear whether his backing is strong enough and timely enough to persuade the Congressional rank and file.

According to a Democratic aide familiar with the discussions, Reid told Paulson this week that “if McCain didn’t come out for this thing and come out for it quickly, it was going to begin bleeding Republican votes.” Democrats “have a very real concern that opposition [from McCain] is going to drive away potential Republican votes,” this aide said.

Democrats are wholly skeptical of the Bush administration and fear a repeat of 2007, when they were doing much of the heavy lifting for the president as he was looking to pass an immigration package that was resisted by the GOP. At the time, Reid and other Democratic leaders, despite opposition from within their own ranks, ultimately backed and pushed for the Senate’s bipartisan deal. But with Minority Leader Mitch McConnell (R-Ky.) largely absent from the weeks-long debate and Republican infighting between conservatives and moderates led by McCain, the package ultimately died.

Given the hangover from the immigration debate and the uncertainty of the bailout’s effectiveness, Democrats are wary of doing anything that could end up being spun by Republicans as being a “Democratic bill.”

Democrats do not want to give Republicans “a last-ditch chance to bludgeon us,” one Democratic aide said.

Republicans continued their infighting over the rescue plan, particularly in the House where conservative rank-and-file Members became increasingly vocal about their opposition despite a pitch from Vice President Cheney and Paulson.

The lobbying campaign appeared to be no accident. One senior GOP Senate aide said Republican Senate leaders are making the case to their Conference that the ramifications of doing nothing are too great, following through on what was described as Paulson’s sobering assessment of the crisis. This aide said of Paulson’s personal appeal to Senators on Tuesday, “It’s fair to say it convinced a number of Members we needed to act, and we need to act quickly.”

Sen. Judd Gregg (R-N.H.), the ranking member on the Budget Committee, said afterward that Congress cannot address the economic meltdown in a partisan way. It will not get done, he warned, unless Democrats and Republicans work together to craft a solution, and that includes the support of McCain and Obama.

“It has to be bipartisan. There’s no choice,” Gregg said, adding, “I would hope that wherever we end up agreeing to here it includes both presidential candidates being comfortable with it.”

Despite newly applied pressure from the White House — and at least a public appearance of support from leadership — lawmakers emerging from Tuesday’s lunch said no Republican Member has stepped forward to champion the White House’s plan. “I don’t know that anyone is,” Sen. John Thune (R-S.D.) said, adding that leadership is not pushing the $700 billion proposal either. “It’s not like the leadership is getting up and saying, ‘This is the position we’ve got to have.’”

Without an in-house champion and a message that is increasingly seen as dangerous, Republicans said the administration has made little headway in moving the minds of dissenting Republicans. “There are a lot of people who have a lot of questions,” Republican Conference Vice Chairman Sen. John Cornyn (Texas) said after the meeting. “I think we’re at the early stages and a lot of work needs to be done.”