"I think he should step aside," Smith said in an interview with US media. "I think it's become clear that he's not the person to carry the Democratic message."
Smith, the ranking member of the US House Armed Services Committee, said he believes Biden has done a great job throughout his presidency, but added that Democrats need someone who can effectively represent the Democratic party.
Smith mentioned that he thinks Vice President Kamala Harris would be a much better and stronger candidate than Biden.
Earlier on Monday, Biden sent a letter to the Democratic members of Congress to reassure them that he is "firmly committed" to staying in the presidential race despite his poor showing in the first presidential debate last month.
Biden appeared confused and incoherent throughout his first debate with presumptive Republican nominee Donald Trump on June 27, reinforcing rather than refuting ongoing concerns about his cognitive abilities at age 81. His poor performance has led some Democratic politicians and donors to call for his removal as a candidate.
The main contenders expected on the ballot in the November 5 election are Biden and Trump, who have both won enough delegates' votes to be the respective Democratic and Republican parties' presumptive nominees. Trump and Biden are set to debate again on September 10.