The bruising battle for the Democratic presidential nomination continues, after former secretary of state Hillary Clinton narrowly won the state of Kentucky on Tuesday, while Vermont Senator Bernie Sanders took the state of Oregon.
Adopting a more defiant tone than before, Mr Sanders pushed back against suggestions from party leaders that he should exit the race and allow Mrs Clinton to focus on defeating presumptive Republican nominee Donald Trump.
Mr Sanders, in a victory speech in California, said: "Pundits and politicians say Bernie Sanders should drop out, the people of California should not have the right to determine who the next president will be... but we are in till the last ballot is cast."
The latest primary comes after Sanders supporters turned violent at a Democratic convention in Nevada at the weekend, highlighting the deepening rift in the party, and the possibility of unrest in Philadelphia at the national convention in July.
In a statement released on Tuesday, Mr Sanders condemned "any and all forms of violence", but also accused the Democratic leadership of trying to "prevent a fair and transparent process from taking place".
After winning Oregon, he targeted the party leadership again in his speech, saying it had the choice to either "open the doors" and "let the people in" or remain a party with "limited participation and limited energy". He was referring to the support he is getting from millions of Americans compared with Mrs Clinton's more subdued campaign that has depended on larger donors.
Turning his attention to the general election, Mr Sanders highlighted the importance of an energetic campaign, which could help lead to a large voter turnout.
"If the Democratic party wants to be certain that Donald Trump is defeated," he said, "we together are the campaign to do that."
Observers expected Mr Sanders' big win in West Virginia last week to give him momentum for a strong finish in this last leg of the primary race but his defeat in Kentucky took some of the wind out of his sails.
"Most of the circumstances in Kentucky favour Mrs Clinton," said political science professor Stephen Voss, from the University of Kentucky. "She has longstanding ties to the state Democratic Party, including support from multiple factions within it... Many of our social conservatives have remained registered with the Democratic party, which means they tend to pull nomination contests in a moderate direction."
In Oregon, however, Mr Sanders' message of change and alleviating economic hardship struck a chord with voters.
"Oregon Democrats have a strong reform tradition," said political science professor Joseph Lowndes from the University of Oregon. "This is also a state that has been very, very hard hit financially in the last 30 years. These work well for Sanders," he added.
With only nine contests left on the Democratic side, Mr Sanders has virtually no path to victory at this point. He has only 1,528 delegates, while Mrs Clinton is ahead with 2,291 - less than 100 shy of the 2,383 delegates needed.
Meanwhile in the Republican camp, Mr Trump signed a joint fund-raising agreement with the Republican National Committee on Tuesday, as his campaign shifted its focus to the general election.
After an uncontested win in the state of Oregon, Mr Trump now has 1,103 delegates - only 134 delegates short of sealing the deal as his party's nominee.