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 ReidNo, it is not racist to question birthright citizenship McConnell rejects Democrats' 'radical movement' to abolish filibuster Harry Reid: 'Decriminalizing border crossings is not something that should be at the top of the list' MORE (D-Nev.) and Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellDavid Axelrod after Ginsburg cancer treatment: Supreme Court vacancy could 'tear this country apart' Pelosi asks Democrats for 'leverage' on impeachment Democrats press FBI, DHS on response to white supremacist violence 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 BennetThe Hill's Campaign Report: Democratic field begins to shrink ahead of critical stretch The Hill's Morning Report - Trump hews to NRA on guns and eyes lower taxes The Hill's Morning Report - Trump searches for backstops amid recession worries MORE (D-Colo.) and Tom UdallThomas (Tom) Stewart UdallDemocrats object to Interior plans to move BLM out west Democrats, environmentalists blast Trump rollback of endangered species protections Republicans should get behind the 28th Amendment 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.