A leading Democratic activist and former adviser to Hillary Clinton argued on Friday that President Trump's replacement for Supreme Court Justice Ruth Bader Ginsburg will inevitably be "illegitimate."

"Any Supreme Court with a Trump justice confirmed to Ruth Bader Ginsburg’s seat at this point in the calendar would be fundamentally illegitimate, and Democrats must be prepared to act accordingly,"  Brian Fallon, who served as press secretary for the Clinton campaign, tweeted Friday.

Fallon added early Saturday morning that Democrats should add seats to the nation's highest court if the "GOP rams Trump pick" through the Senate.

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His tweets touched on widespread criticism of the idea that Republicans in the Senate could push through a Supreme Court nominee's confirmation just weeks before the 2020 elections.

On Friday, Clinton herself told MSNBC that Senate Majority Leader Mitch McConnell, R-Ky., would be erecting a "monument to hypocrisy" if he pushed through Trump's nominee, citing his decision to block former President Obama's nominee, Judge Merrick Garland, before the 2016 election.

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Fallon, who leads the group "Demand Justice," previously argued that the confirmations of Supreme Court Justices Brett Kavanaugh and Neil Gorsuch weren't "legitimate" either. Under PresidentTrump's administration, Fallon's group has lodged a series of attacks on Kavanaugh.

For example, his group previously set up an ad campaign targeting law firms that paid for a group "rebuilding Kavanaugh's image." He also led a failed effort to prevent George Mason University from hiring Kavanaugh as a visiting professor at its law school.