Sen. Al FrankenAl FrankenFriends, foes spar in fight on Trump’s Supreme Court nominee Lawmakers share photos of their dogs in honor of National Puppy Day Franken challenges witness endorsement of Gorsuch MORE (D-Minn.) said in an interview broadcast Sunday that he is "sure" there will be challengers to Hillary ClintonHillary Rodham ClintonDemocrats step up calls that Russian hack was act of war Comet Ping Pong shooter pleads guilty Time for 'J. Edgar' Comey to take his leave 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 SandersBernie SandersSanders will 'absolutely' work with Trump to lower prescription drug costs Sanders says he will introduce 'Medicare for all' bill Sunday shows preview: Aftermath of failed healthcare bill MORE (I-Vt.) and Elizabeth WarrenElizabeth WarrenDems question potential Kushner real estate deal with Chinese firm Inspector general reviewing HHS decision to halt ObamaCare ads Warren: 'Today is a great day... but I'm not doing a touchdown dance' 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 CruzHow 'Big Pharma' stifles pharmaceutical innovation AIPAC must reach out to President Trump Under pressure, Dems hold back Gorsuch support 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.