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 ReidBernie campaign 2.0 - he's in it to win it, this time around Dems wrestle over how to vote on ‘Green New Deal’ Senate confirms Trump court pick despite missing two 'blue slips' MORE (D-Nev.) and Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellTrump blasts McCain, bemoans not getting 'thank you' for funeral GOP senator: Trump's criticism of McCain 'deplorable' McConnell calls McCain a 'rare patriot' and 'American hero' after Trump criticism 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 BennetCourt-packing becomes new litmus test on left New England Patriots player says he will remain in locker room during anthem next season Press: Which way do Dems go in 2020? MORE (D-Colo.) and Tom UdallThomas (Tom) Stewart UdallOvernight Energy: DC moves closer to climate lawsuit against Exxon | Dems call for ethics investigation into Interior officials | Inslee doubles down on climate in 2020 bid Dem lawmakers call for investigation into Interior officials over alleged ethics violations The Hill's 12:30 Report: Manafort sentenced to total of 7.5 years in prison 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.