President Obama told Democratic donors he might be "in a very strong position" to demand a Constitutional amendment on campaign finance reform during his second term, according to a new book.

The president made the comments at a closed-door, high-dollar 2012 fundraiser in Seattle, where supporters included the likes of billionaire Microsoft founder Bill Gates.

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"Now, I taught constitutional law. I don't tinker with the Constitution lightly. But I think this is important enough that citizens have to get mobilized around this issue, and this will probably be a multiyear effort," Obama said, according to an excerpt from Big Money by journalist Ken Vogel, obtained by Mother Jones.

"After my reelection, my sense is that I may be in a very strong position to do it," Obama continued.

Later that year, the president publicly endorsed a constitutional amendment that would overturn the controversial Citizens United decision that allowed unlimited political spending by outside groups.

“Over the longer term, I think we need to seriously consider mobilizing a constitutional amendment process to overturn Citizens United (assuming the Supreme Court doesn't revisit it)," Obama wrote during a question-and-answer session on Reddit.

“Even if the amendment process falls short,” he said, “it can shine a spotlight of [sic] the super-PAC phenomenon and help apply pressure for change.”

On Tuesday, 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.) and Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellSchumer: Trump's team made case for new witnesses 'even stronger' Trump, Democrats risk unintended consequences with impeachment arguments CNN's Axelrod says impeachment didn't come up until 80 minutes into focus group MORE (R-Ky.) appeared before the Senate Judiciary Committee to debate a proposed constitutional amendment to regulate campaign spending.

The amendment, drafted by Sens. Michael BennetMichael Farrand BennetSunday shows preview: Lawmakers prepare for week two of impeachment trial Impeachment throws curveball in Iowa to sidelined senators Sanders says it's 'disappointing' he's not on campaign trail in Iowa MORE (D-Colo.) and Tom UdallThomas (Tom) Stewart UdallIt is time for companies and governments to holistically tackle single-use plastics Citizens United decision weathers 10 years of controversy Overnight Defense: Foreign policy takes center stage at Democratic debate | House delivers impeachment articles to Senate | Dems vow to force new vote on Trump's border wall MORE (D-N.M.), would allow Congress to regulate and limit spending on federal campaigns, including expenditures from outside groups. The proposal would also allow states to regulate campaign spending for their races.

Senate Democrats have sought to make outside spending a primary issue ahead of November's midterm elections, with Reid frequently railing against billionaire GOP donors like Charles and David Koch.

Republicans have said the proposed amendment would undermine First Amendment rights.