A rogue musical instrument almost had Sen. Tim Kaine Timothy (Tim) Michael KaineBiden promises Democratic senators help in battleground states Second GOP senator to quarantine after exposure to coronavirus The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-Va.) singing the blues when one of the former vice presidential nominee’s harmonicas set off an airport metal detector.

A TSA agent stopped Kaine after his bag rolled through the X-ray machine at Ronald Reagan Washington National Airport on Thursday afternoon.

The security pro asked Kaine, who was traveling with his wife, Anne, if the bag belonged to him and said he needed to examine it, according to an ITK tipster who was standing by Kaine in line.

Just as our spy was slipping a coat back on, they heard a harmonica playing, and saw the Kaines and the TSA agent cracking up laughing.

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“That’s when I figured out, ‘Oh my God, his freaking harmonica set off the metal detector,’ ” our source exclaimed.

The senator — who we hear carries as many as five harmonicas at a time — appeared unfazed in the midst of the musical security snafu, shaking well-wishers' hands before being cleared to head to his flight.

Kaine, who learned to play his mouth organ around seventh grade, frequently featured his harmonica prowess while on the campaign trail with former Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonHillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters FBI chief says Russia is trying to interfere in election to undermine Biden MORE last year. The VP hopeful busted out the instrument everywhere from an appearance on “Ellen” to a campaign stop at a brewery in North Carolina.

A seemingly amused Kaine spokeswoman declined to comment on the harmonica brouhaha.