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 ReidLobbying World Mitch McConnell is not invincible Seven big decisions facing Biden in 2020 primary MORE (D-Nev.) and Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellThe Hill's Morning Report - Trump says no legislation until Dems end probes Threat of impeachment takes oxygen out of 2019 agenda Chances for disaster aid deal slip amid immigration fight 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 BennetCNN's O'Rourke town hall finishes behind Fox News, MSNBC The Hill's Morning Report - White House, Congress: Urgency of now around budget Overnight Energy: Warren wants Dems to hold climate-focused debate | Klobuchar joins candidates rejecting fossil fuel money | 2020 contender Bennet offers climate plan MORE (D-Colo.) and Tom UdallThomas (Tom) Stewart UdallOvernight Defense: Iran worries dominate foreign policy talk | Pentagon reportedly to send WH plans for 10K troops in Mideast | Democrats warn Trump may push through Saudi arms sale | Lawmakers blast new Pentagon policy on sharing info Senate panel rejects requiring Congress sign off before Iran strike Democrats grill Trump Interior chief for saying he hasn't 'lost sleep' over climate change 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.