The debate about the pull that wealthy donors have in politics is set to take center stage on the Senate floor this week as Democrats push a constitutional amendment that would give lawmakers more leverage to restrict campaign financing and spending.

The longshot measure -- dubbed by supporters the Democracy for All Amendment -- is an attempt to provide elected officials with a legal authority to curb the big money that has buoyed super PACs and politically active tax-exempt groups since the Supreme Court’s 2010 Citizens United decision.

The bill, sponsored by Sen. Tom Udall (D-N.M.), says that Congress and the states can “set reasonable limits on the raising and spending of money by candidates and others to influence elections.” It also gives federal and state authorities the power to prohibit election spending by corporations, which was permitted by Citizens United.

The amendment faces steep odds: it would require the support of two-thirds of the House and the Senate, and then would have to be ratified by three-quarters of the states.

But it is being seized upon by both the left and right as a way to engage in a proxy fight over the role of money in politics -- a major theme of this year’s midterm elections, in which billionaire donors such as Charles and David Koch and Tom Steyer have played starring roles in campaign ads. Already, outside groups have reported spending nearly $200 million on this year’s races, according to the Center for Responsive Politics, a nonpartisan research organization. That's more than triple this point in the 2010 midterms.

Both sides are seeking to make the most of the Senate vote. Backers of the constitutional amendment are set to hold a rally on Capitol Hill Monday afternoon with Democratic senators to showcase three million signatures they have gathered in support. Meanwhile, the Republican senators are planning to use the floor debate over the bill to spotlight the role of wealthy liberal donors.

Supporters of the amendment have sought to emphasize its bipartisan appeal. Udall joined with former Sen. Alan Simpson (R-Wy.) in an op-ed published Monday by The Hill to argue it is necessary to change a system in which “a few billionaires can drown out the voices of millions of Americans.”

But the debate is likely to break sharply along partisan lines. The measure has 48 co-sponsors -- none of them Republican. Senate Minority Leader Mitch McConnell has attacked the bill as an assault on free speech protections. The goal of the Democrats, he wrote in a piece for Politico, “is to shut down the voices of their critics at a moment when they fear the loss of their fragile Senate majority.”

The absence of GOP support for the bill underscores a substantial shift within the party on campaign finance issues over the last several decades. Past versions of the constitutional amendment -- which has been introduced in various forms beginning in 1986 -- have been cosponsored by Republicans such as Sen. Ted Stevens of Alaska, Sen. Arlen Specter of Pennsylvania, Sen. Thad Cochran of Mississippi and Sen. John McCain of Arizona.