Democratic presidential candidate Bernie Sanders vowed on Thursday to prevent Republican Donald Trump from becoming the U.S. president amid concerns about further damage to party unity deriving from his continued stay in the race.

"Needless to say, I am going to do everything in my power, and I will work as hard as I can to make sure Donald Trump does not become president of the United States," said Sanders here after his meeting with U.S. President Barack Obama.

Meanwhile, Sanders said he already talked with Hillary Clinton after Clinton amassed enough delegates needed to notch up the nomination on Tuesday and he said they would speak soon about how to "work together" to defeat Trump.

However, Sanders still declined to endorse Clinton at the moment and insisted that he would take part in the last nomination contest next week. 

source : xinhua