Just as Senator Bernie Sanders began to address an audience of thousands at an event in Seattle, a group of activists stormed the stage and grabbed the microphone.
The protesters, who identified with the Black Lives Matter movement that was born of a series of high-profile killings of black men by US police officers last year, prevented Sanders from actually delivering a speech.
The 73-year-old Sanders, who is running against Hillary Clinton to become the Democratic party's presidential candidate, could not convince the protesters to surrender the stage and decided instead to wait a few minutes for them to finish.
Two women spoke about events in Ferguson, Missouri, where black teenager Michael Brown was shot dead by a white police officer a year ago, and held a four and a half minute of silence.
Marissa Johnson, left, and Mara Jacqueline Willaford take over the microphone from Bernie sanders
When the crowd called for Sanders to speak, one of the women reportedly called them "white supremacist liberals".
After 20 minutes waiting, Sanders tried to restart his rally, but was pushed aside once again. He then left the stage, waving goodbye before shaking hands and posing for pictures for about 15 minutes.
Sanders later delivered the speech he had prepared to a crowd of around 15,000, pledging to fight for 12 weeks of paid leave for new parents, a minimum wage of $15 an hour, and equal pay for women.
In a formal statement addressing the protest, Sanders said he was "disappointed that two people disrupted a rally attended by thousands […] I was especially disappointed because on criminal-justice reform and the need to fight racism there is no other candidate for president who will fight harder than me."
Saturday's speech was not the first time the Vermont senator has been targeted by Black Lives Matters supporters.
Last month, at a town hall for Democratic presidential candidates, a group of people affiliated with the movement seized the stage and disrupted an interview with Sanders and former Maryland Governor Martin O'Malley.
