(CNN) In a sign of Amy Klobuchar's determination to stop Bernie Sanders from becoming the Democratic presidential nominee, her campaign argued in a memo released Monday that the Minnesota senator is the moderate best positioned to beat him.

"Just as Amy has shown on the debate stage, she is the best person to take on Bernie Sanders and the best candidate to beat Donald Trump," campaign manager Justin Buoen wrote in the memo. "Both ​on​ and ​off​ the debate stage, Amy has highlighted the consequences of having Bernie Sanders lead the top of the ticket, including his divisive politics and health care plan that would kick 149 million Americans off their insurance."

Monday's memo announced an additional $4.2 million ad buy in Super Tuesday states on cable, broadcast & digital, supplementing existing buys.

The memo points to raw vote totals, where Klobuchar is in third behind Sanders and former South Bend, Indiana, Mayor Pete Buttigieg. It also cites that Klobuchar currently has 7 delegates, one behind Massachusetts Sen. Elizabeth Warren.

A senior Klobuchar campaign adviser said the memo was not a direct response to calls for Klobuchar to drop out of the race.

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