Former Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.) said Tuesday that he believes former Vice President Joe Biden Joe BidenOmar fires back at Trump over rally remarks: 'This is my country' Trump mocks Biden appearance, mask use ahead of first debate Trump attacks Omar for criticizing US: 'How did you do where you came from?' MORE is the Democrat who should most worry Republicans heading into the 2020 presidential election.

"Joe Biden is, I think that strikes fear in a lot of Republicans," Flake said on "CBS This Morning," where he is a contributor.

"He can speak to those states that President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE won in the Rust Belt in particular, and he’s seen as more of a centrist," Flake added. "He was a senator for 30-some years. He knows how to work with the Senate with the Congress and I think that’s certainly one that worries Republicans."

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"Joe Biden strikes fear in a lot of Republicans. He can speak to those states that Pres. Trump won... and he’s seen as more of a centrist. He knows how to work with the Senate, with the Congress, and I think that’s certainly one that worries Republicans." -- @JeffFlake pic.twitter.com/b1IcZxOBr1 — CBS This Morning (@CBSThisMorning) March 12, 2019

Biden has been mulling a potential 2020 campaign for months, and sources familiar with his plans have told The Hill that he is nearly certain to jump into the race. The former vice president said late last month that his family wants him to run.

Sens. Elizabeth Warren (D-Mass), Kamala Harris (D-Calif.), Kirsten Gillibrand (D-N.Y.), Cory Booker (D-N.J.), Amy Klobuchar (D-Minn.) and Bernie Sanders (I-Vt.) are among those who have already entered the race for a chance to take on President Trump next year.

Biden has long hovered at or near the top of polling among Democrats on their preferred 2020 candidate. A poll released last month by the left-leaning Public Policy Polling firm showed Biden and Trump in a statistical dead heat in a hypothetical 2020 match-up.