Bernie SandersBernard (Bernie) SandersWorld leaders reach agreement on trade deal without United States: report Sanders on Brazile revelations: DNC needs ‘far more transparency’ Sen. Warren sold out the DNC MORE's lone supporter in the Senate is flipping to back Hillary ClintonHillary Diane Rodham ClintonGOP rushes to cut ties to Moore Papadopoulos was in regular contact with Stephen Miller, helped edit Trump speech: report Bannon jokes Clinton got her ‘ass kicked’ in 2016 election MORE for president. 

Sen. Jeff MerkleyJeffrey (Jeff) Alan MerkleyDems mull big changes after Brazile bombshell Dems push clearer GMO labeling Dems cheer Flake after scathing Trump speech MORE (D-Ore.), the only senator to endorse Sanders, on Friday told CNN he would back Clinton just days after she became the party's presumptive nominee. 

"Certainly, I'm going to be supporting our nominee and our nominee is Secretary Clinton," Merkely told CNN. 

He also said Sen. Elizabeth WarrenElizabeth Ann WarrenBipartisan group of lawmakers aim to reform US sugar program Schumer: Dems want DACA fix in government spending bill The Hill interview — DNC chief: I came here to win elections MORE (D-Mass.) would be a "wonderful vice presidential choice." 

Merkley earlier this week urged Sanders to rethink his campaign and back Clinton to unify the party before the general election, but he hadn't yet formally endorsed her until Friday. 

When Merkley endorsed Sanders in April, he said he was "boldly and fiercely addressing the biggest challenges facing our country."   

Clinton has won a number of big victories this week. She became the presumptive nominee after winning the California primary and has taken a commanding lead with the party's superdelegates, and she's been endorsed by President Obama, Vice President Biden and Warren.

Sanders, who met with Obama at the White House on Thursday, is continuing his campaign, but has dramatically softened his rhetoric in recent days, leading onlookers to believe he no longer plans to try to contest the Democratic convention in July.