(CNN) Iowa. New Hampshire. Donor enclaves on the coasts. And... the Ed Sullivan Theater?

Yes, the home of Stephen Colbert's "Late Show" is proving to be a key stop for Democrats who are positioning themselves for 2020 presidential bids.

Sen. Bernie Sanders sat down with Colbert one month ago. So did former HUD secretary Julián Castro. Sen. Kamala Harris was there last week. And Sen. Kirsten Gillibrand is expected to share some news about her presidential aspirations in an interview on Tuesday's show.

It will be Gillibrand's second appearance in just over two months. When she was on the "Late Show" two days after the midterms, she said she was giving "long hard thought" to a 2020 run.

Colbert's studio is a logical place for Democrats to tease presidential campaign plans. He has a liberal fan base dating back to his days on Comedy Central, and that audience crystallized after Colbert took aim at then-candidate Donald Trump in 2016.

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