Washington (CNN) Susan Rice, who was President Barack Obama's national security adviser, caused a stir Friday afternoon when she tweeted "Me" when another former Obama official asked who could challenge Sen. Susan Collins in 2020.

The short tweet -- which came less than an hour after Collins, a Maine Republican, announced she would vote to confirm Brett Kavanaugh to the Supreme Court -- caught national and state Democrats by surprise.

Rice tweeted a little later that she was "not making any announcements" but was "deeply disappointed" by Collins' vote.

Rice has a home in Maine, a source said, and her family has ties to the state: Her mother, an education policy expert who was instrumental in the creation of the Pell Grant, was born there.

Rice's "Me" tweet was a response to another Obama-era official, Jen Psaki, tweeting: "who wants to run for Senate in Maine? there will be an army of supporters with you."

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