Senator Bernie Sanders said on Sunday that he would “take our campaign for transforming the Democratic Party into the convention,” refusing to concede the presidential nomination to Hillary Clinton though not explicitly saying he would challenge her for it.
Mrs. Clinton earned enough delegates to clinch the nomination last week, but Mr. Sanders has declined to end his campaign. He has contended that he could persuade enough superdelegates, the party leaders who have overwhelmingly backed Mrs. Clinton, to switch their support to him by arguing that he would be the stronger candidate against Donald J. Trump, the presumptive Republican presidential nominee.
That plan became more improbable last week as high-profile Democrats supported Mrs. Clinton. President Obama endorsed her on Thursday, calling her the most qualified candidate ever to seek the White House and imploring Democrats to unite behind her. Vice President Joseph R. Biden Jr. and Senator Elizabeth Warren of Massachusetts also endorsed Mrs. Clinton. Senator Jeff Merkley of Oregon, the only senator to endorse Mr. Sanders, told CNN on Friday that he now supports Mrs. Clinton.
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