The Senate should take up stalled campaign finance legislation during the lame-duck session after next month's elections, a Democratic senator said Monday. 

Sen. Claire McCaskillClaire Conner McCaskillHow Citizens United altered America's political landscape #MidnightMoscowMitch trends amid criticism of McConnell's proposed impeachment trial rules The most expensive congressional races of the last decade MORE (D-Mo.) argued that the legislation, called the Disclose Act, is necessary to bring more transparency to outside spending in politics, a topic Democrats have harped on during the final weeks of the midterm campaign.

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"I think we should do it in lame-duck; I think we should do it next year. I don't care when we do it," McCaskill said on MSNBC's "Morning Joe."

McCaskill's call underscores Democrats' criticism of spending by outside groups, such as the U.S. Chamber of Commerce, on behalf of Republican candidates this cycle, during which the GOP is expected to make large gains on Democratic majorities in Congress.

The Disclose Act, which is intended as a response to a Supreme Court decision earlier this year that relaxed limits on political spending by corporations and unions, would require those entities to file detailed public reports on political spending. The legislation passed the House, but two separate efforts to bring it to a vote in the Senate failed after centrist Republican senators declined to support it.

Senate Majority Leader Harry ReidHarry Mason ReidTensions between McConnell and Schumer run high as trial gains momentum The Trumpification of the federal courts Trump to rally evangelicals after critical Christianity Today editorial MORE (D-Nev.) has not said whether it will be brought up during the lame-duck session, which begins Nov. 15.

President Obama for months has called on Congress to pass the legislation and recently has led Democratic criticism of outside spending by GOP groups. They have complained that the nonprofit groups should reveal the identity of their donors, pointing out that some groups, like the U.S. Chamber of Commerce, have taken money from foreign entities.

Democrats have railed against Republicans for obstructing the measure they say will help keep reasonable limits on outside political spending by requiring transparency and disclosure of expenditures, but the GOP has said that it does not apply evenly to all outside entities.

The Chamber has fired back at Democrats, saying that they do not use foreign contributions from members for political purposes, which would be illegal. Outside groups have largely said they will not disclose the identity of their donors unless it is required by law. They have also accused Democrats of hypocrisy, pointing out that they accepted large amounts of outside money during the 2008 campaign.

McCaskill made it clear that "I'm not saying that anything going on right now is illegal," but said that bringing greater "transparency" to campaign finance is a key step toward "reforming Washington."