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 ReidThe Hill's 12:30 Report - Presented by Connected Commerce Council - Biden faces reporters as his agenda teeters Biden hits one-year mark in dire straits 'All or nothing' won't bolster American democracy: Reform the filibuster and Electoral Count Act MORE (D-Nev.) and Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellThese Senate seats are up for election in 2022 WATCH: The Hill recaps the top stories of the week Effort to overhaul archaic election law wins new momentum 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 BennetThese Senate seats are up for election in 2022 Overnight Energy & Environment — Starting from 'scratch' on climate, spending bill Eight senators ask Biden to reverse course on Trump-era solar tariffs MORE (D-Colo.) and Tom UdallTom UdallCruz to get Nord Stream 2 vote as part of deal on Biden nominees Democrats threaten to play hardball over Cruz's blockade Rubio vows to slow-walk Biden's China, Spain ambassador nominees 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.