The 2020 field is packed with senators. Senators usually don't win the White House.

Sen. Amy Klobuchar (D-Minn.) launched her 2020 presidential bid Sunday, joining fellow Sens. Elizabeth Warren (Mass.), Kamala Harris (D-Calif.), Cory Booker (D-N.J.), and Kirsten Gillibrand (D-N.Y.) as well as Rep. Tulsi Gabbard (D-Hawaii) in seeking the Democratic nod. Unfortunately for all six, congressional office is historically not a great stepping stone to the presidency.

As a FiveThirtyEight analysis details Monday, only about one in three senators and representatives who have secured their party's presidential nomination have won the White House. By contrast, half of nominees who previously served as vice president, governor, or in a Cabinet-level role — particularly secretary of state — won their general elections.

Before former Vice President Joe Biden gets his hopes up, however, FiveThirtyEight offers a word of caution. In the last six decades, "three of the seven most recent vice presidents later won their party’s nomination for president," but "only one (George H.W. Bush) made it to the Oval Office." Experience as veep may not provide the level of campaign viability it once did.

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There's also the question of viability in the primary race. On this point, former vice presidents and governors are most likely to prevail. Hillary Clinton's nomination in 2016 was the first such victory by a Cabinet-level official in nearly a century.

Members of Congress may have a more difficult time in both the primaries and the general election, FiveThirtyEight suggests, because Congress is generally unpopular and their voting records offer ample opportunities for attack.