Katy Perry Wears Kamala Harris Merch After Taylor Swift Endorsement

Taylor Swift isn't the only pop star publicly endorsing Kamala Harris ... Katy Perry stepped out in some merch supporting the Vice President's presidential run Wednesday.

Hours after Taylor Swift announced her endorsement of Harris and Tim Walz's campaign for the White House, the fellow singer stepped out in Manhattan wearing a camo-patterned Harris-Walz hat.

While it's no secret that Katy leans liberal -- she previously shared a video compilation of Harris highlights set to her hit "Woman's World" this summer -- her outing makes it clear she's all in on supporting the Harris-Walz ticket.

Katy is probably just showing her support for Harris after her killer performance during Tuesday night's debate against Donald Trump ... but some fans are speculating KP is trying to steal some of Taylor's thunder in the aftermath of Swift's highly publicized endorsement.

As TMZ previously reported ... Taylor had remained surprisingly tight-lipped throughout most of the campaign -- even after Trump pushed out fake AI imagery suggesting she was supporting him.

But after Tuesday's debate, the "Cruel Summer" singer spoke out on social media ... declaring her support for Harris and taking subtle jabs at Trump and his running mate, J.D. Vance.

Countless celebrities showed their love on Taylor's online announcement ... with Olivia Wilde, Kylie Kelce, Hilary Duff, Christie Brinkley, Demi Lovato, Blake Lively, Lady Gaga and others all hitting the like button.

Katy, however, did not press like on Taylor's post ... despite following her former frenemy on Instagram.

Taylor and Katy have a complicated history ... which includes dating the same guy -- John Mayer -- and writing diss tracks about one another. The 2 seemed to bury the hatchet when Katy sent a literal olive branch to Taylor back in 2018.