Biden and Harris share another impromptu encounter
© Twitter

They could soon be facing off in the 2020 Democratic primary, but for now, Sen. Kamala HarrisKamala Devi HarrisWarren unveils plan to cancel student loan debt, create universal free college Moulton enters 2020 White House race The Hill's Morning Report - Is impeachment back on the table? MORE and Joe BidenJoseph (Joe) Robinette BidenWarren unveils plan to cancel student loan debt, create universal free college Moulton enters 2020 White House race The Hill's Morning Report - Is impeachment back on the table? MORE are facing each other — bumping into one another for the second time in as many months.

An aide for the California Democrat — who launched her presidential bid last month — tweeted a photo Thursday of her boss engaged in a chance encounter on the train with the former vice president:

Harris’s sister also shared a snapshot of Biden and the senator, who appeared to be exchanging pleasantries:

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Back in December, Harris’s communications director, Lily Adams, tweeted, “You just never know who you might run into in DC…” with a photo of the two political VIPs smiling together.

Recent polling showed Biden — who has not announced any plans to run — at the top of a field of potential 2020 Democratic candidates in Iowa. In the poll, Biden led Harris, his closest competitor, by 11 points.