Big news on impeachment this week, or not: On Monday Ben Ray Luján, the number four Democrat in House leadership, endorsed “an impeachment inquiry, which will continue to uncover the facts for the American people and hold this president accountable.” The press played it as a big moment, the highest-ranking Democrat to endorse the probe.

“President Trump’s lack of action is jeopardizing our elections, national security, and Democracy,” Mr. Luján said in explaining his decision. “Not only has he ignored the warnings that our Democracy is being targeted, but he has also actively encouraged Russian interference.” But wait. Special counsel Robert Mueller released his report in April. Why reach this conclusion four months later?

You have to read 15 paragraphs into the Politico story on Mr. Luján’s conversion to discover the real reason. The New Mexico Congressman is running for the Senate to replace Democrat Tom Udall and he faces two liberal primary challengers. One competitor, New Mexico Secretary of State Maggie Toulouse Oliver, called on the House to start impeachment proceedings in May.

“First it was the Green New Deal, then it was Medicare for All and not taking any more corporate money,” Ms. Toulouse Oliver said. “Today it’s impeachment. I’m glad to see the Congressman adopting progressive values, but New Mexico deserves a U.S. Senator who will lead on the issues that truly matter.”

Mr. Luján is merely protecting his left flank. And far from challenging Speaker Nancy Pelosi’s opposition to impeachment, he no doubt had her blessing.