Senate Republicans are moving to keep the Supreme Court at nine justices as a growing number of Democratic 2020 contenders have expressed an openness to expanding it. 
 
Roughly a dozen Republican senators introduced the resolution on Monday that would keep the Supreme Court at nine justices. 
 
"The Democrats' court-packing proposal represents the latest shortsighted effort to undermine America's confidence in our institutions and our democracy," Sen. Marco RubioMarco Antonio RubioThe Hill's 12:30 Report — Presented by MAPRx — Trump jumps into 2020 race The Hill's 12:30 Report — Presented by MAPRx — Trump jumps into 2020 race GOP frets about Trump's poll numbers MORE (R-Fla.), who spearheaded the resolution, said in a statement.
 
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He added that he was introducing the constitutional amendment "to prevent the delegitimizing of the Supreme Court."
 
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The Senate resolution would specify that the Supreme Court "shall be composed of not more than 9 justices." A similar resolution was introduced in the House late last week. 
 
Enacting a constitutional amendment would be an uphill battle, if not an impossible goal. The amendment would first need to win over two-thirds of both chambers of Congress, and then be ratified by three-fourths of the states.
 
But Rubio first announced last week that he would introduce the amendment after several Democratic White House contenders, including a handful that are Rubio's Senate colleagues, expressed an openness to expanding the Supreme Court or enacting other judicial reforms, including term limits. 
 
Both Sens. Elizabeth WarrenElizabeth Ann WarrenSanders denies tweet about corporate Democrats was dig at Warren Sanders denies tweet about corporate Democrats was dig at Warren Warren: 'On Juneteenth and every day: Black lives matter' MORE (D-Mass.) and Kamala HarrisKamala Devi HarrisDemocrats asked to create ideal candidate to beat Trump pick white man: poll Democrats asked to create ideal candidate to beat Trump pick white man: poll Biden defends remarks about segregationist senators: 'Apologize for what?' MORE (D-Calif.) have said expanding, or "packing," the court should be an option on the table as part of a larger conversation among Democrats about the direction of the U.S. judicial system.

 
Supporters argue that President TrumpDonald John TrumpBooker hits Biden's defense of remarks about segregationist senators: 'He's better than this' Booker hits Biden's defense of remarks about segregationist senators: 'He's better than this' Trump says Democrats are handing out subpoenas 'like they're cookies' MORE and congressional Republicans have been able to pack the courts with conservative judges, including two Supreme Court justices and dozens of appeals court nominees.

But Rubio countered in a Fox News op-ed last week that trying to expand the courts had become a "litmus test" for White House hopefuls and stemmed from an "ugly, winner-take-all rhetoric" among progressives.