Sen. Al FrankenAlan (Al) Stuart FrankenTrump quietly putting his stamp on the courts Grassley shouldn't allow Senate Democrats to block judicial nominees Senate Dems push Trump admin to protect nursing home residents' right to sue MORE (D-Minn.) said in an interview broadcast Sunday that he is "sure" there will be challengers to Hillary ClintonHillary Rodham ClintonAssange meets U.S. congressman, vows to prove Russia did not leak him documents High-ranking FBI official leaves Russia probe OPINION | Steve Bannon is Trump's indispensable man — don't sacrifice him to the critics MORE in the Democratic presidential primary. 

Asked on CNN's "State of the Union" if Democrats need a spirited primary, Franken said of Clinton, "I very much doubt that she’ll be the only one. I’m sure someone will jump in."

"I don’t know how you make someone else viable, they have to make themselves viable, but I’m sure that there will be a number of other people in the race," Franken added. 

Clinton is by far the frontrunner for the Democratic nomination. Other names that have surfaced for a run are Sens. Bernie SandersBernard (Bernie) SandersThe media couldn't be more blatant in distorting Trump's words on Charlottesville Road to renewable energy is filled with potholes of ‘magic thinking’ Bernie Sanders: Trump’s Charlottesville comments ‘embarrassing’ MORE (I-Vt.) and Elizabeth WarrenElizabeth WarrenWarren: Education Dept lawyer may have violated conflict-of-interest laws Congress should think twice on the Israel Anti-Boycott Act Sanders plans to introduce single-payer bill in September MORE (D-Mass.), though Warren denies she will run. Maryland Gov. Martin O'Malley (D) is also a possibility. 

Franken reflected on the lesson of the midterms by saying Democrats need to fight for the middle class while also working across party lines. 

After his razor-thin 2008 victory, the former "Saturday Night Live" star said, "There were, I think, a lot of Minnesotans who didn’t quite know what to expect, but what they saw is I worked every day in what I saw as the interests of Minnesotans, and I worked across party lines to find common ground."

"While I found common ground, I stood my ground when the powerful would come after the middle class or those aspiring to be in the middle," Franken said. 

Franken, a leading proponent of net neutrality rules for the Internet, also hit back against Sen. Ted CruzTed CruzThe media couldn't be more blatant in distorting Trump's words on Charlottesville Curtis wins GOP primary for House seat vacated by Jason Chaffetz Kimmel: Let’s make Trump a king so he has no power MORE (R-Texas), who called net neutrality "ObamaCare for the Internet."

"He has it completely wrong and just doesn't understand what this issue is," Franken said.