Sen. Jeff Merkley (D-Ore.), the only U.S. Senator to endorse Democratic presidential candidate Sen. Bernie Sanders (D-Vt.), still plans to vote for Sanders at the Democratic National Convention.

But just on the first ballot.

In recent days, Merkley has urged Sanders to back presumptive Democratic nominee Hillary Rodham Clinton. But Merkley's office tells WW that the senator still plans on casting his superdelegate vote for Sanders—if only as a symbolic gesture.

"If there's a contested vote at the convention," says spokeswoman Courtney Crowell, "Senator Merkley would still cast his ballot on the first vote for Senator Sanders as a way of representing his support for the vision and priorities Bernie campaigned on."

Merkley is the only Oregon superdelegate who pledged support to Sanders before the state's May primary.

The explanation comes hours after President Obama met with Sanders at the White House and subsequently endorsed Hillary Clinton in an online video.

Merkley had announced his support for Sanders through an April op-ed column for The New York Times, in which he also predicted Clinton would be a "strong and capable president."

"Once a candidate has won a majority of the pledged delegates and a majority of the popular vote, which Secretary Clinton has now done, we have our nominee," Merkley told the Post. "This is the moment when we need to start bringing parts of the party together so they can go into the convention with locked arms and go out of the convention unified into the general election."