When asked to respond to the massive crowds that Democratic presidential hopeful Sen. Bernie Sanders (I-Vt.) is drawing to his campaign events, White House spokesman Josh Earnest called it “a good sign.”

The socialist senator surging in the polls attracted about 7,500 people to a stump speech in Portland, Maine on Monday night. More than 10,000 showed up at a similar event for Sanders in Madison, Wis. last week, raising the specter among establishment Democrats that he could seriously challenge Hillary Clinton—the administration’s former Secretary of State.

“It’s clear that there’s a lot of energy on the Democratic side of the aisle and I think that is a good thing,” Earnest said, adding that “seeing a lot of democratic leaning voters charged up and excited about politics and participating in a political event is something that we’re pleased to see.”

Earnest, however, was careful not to speak about the prospect of a Sanders victory in light of the crowds.

“What impact that has on the candidacy of one candidate or another is something I’ll leave to all of you,” he told reporters, without mentioning either Sanders or Clinton by name.

While serving in the Senate, Sanders has often played foil to the Obama administration’s policy maneuvering on economic issues, even “filibustering” legislation the President supported in 2010 to extend the Bush tax cuts.