Bernie Sanders has landed his biggest endorsement yet — and his first from a fellow Democratic senator.

Oregon Sen. Jeff Merkley published an op-ed in the New York Times on Wednesday morning saying he would be supporting Sanders for a number of reasons, including the Vermont senator's positions on energy reform, predatory lending, and international trade deals.

But perhaps the most interesting sentence of the editorial is the one in which Merkley says he's endorsing Sanders not just because of his positions on policy issues, but because he agrees with Sanders's means of achieving them and his critique of the current system.

"People know that we don’t just need better policies, we need a wholesale rethinking of how our economy and our politics work, and for whom they work," Merkley writes. "We need urgency. We need big ideas. We need to rethink the status quo."

This closely reflects Sanders's conception of a "political revolution," even if it uses the softer term "wholesale rethinking." In his op-ed, Merkley is signaling his support for that more sweeping theory of change.

Hillary Clinton still has the endorsements of an overwhelming number of Democrats in both Congress and state offices. The Times reported in February that Clinton has been endorsed by 40 Democratic senators while Sanders still had none — until today.

Merkley is also one of the most liberal members of Congress, and he comes from a heavily white state that is overwhelmingly likely to vote for Sanders in its May 17 primary. If anyone in Congress was likely to support Sanders's insurgency, it was Merkley.

"Sanders is boldly and fiercely addressing the biggest challenges facing our country," Merkley wrote. "His leadership on these issues and his willingness to fearlessly stand up to the powers that be have galvanized a grass-roots movement."

Still, Merkley's endorsement shows that the party establishment may not be as uniformly behind Clinton as it first appeared. And it suggests Sanders is persuading Democratic officials, and not just millions of voters, that his preferred path for the party is the right one.