Sen. Bernie Sanders', I-Vt., former presidential campaign press secretary tweeted she is not throwing support behind the likely Democrat presidential nominee Joe Biden, minutes after her former boss endorsed the former vice president in an online video.

In the video, Sanders and Biden talked about developing a strategy on how to beat President Donald Trump in the November election.

Briahna Joy Gray worked as Sanders' national spokeswoman until the candidate shelved his campaign last week.

Minutes after the video appeared online, Gray tweeted:

"With the utmost respect for Bernie Sanders, who is an incredible human being & a genuine inspiration, I don't endorse Joe Biden. I supported Bernie Sanders because he backed ideas like #MedicareForAll, cancelling ALL student debt, & a wealth tax. Biden supports none of those."

Gray's message amplified the sentiments of many Sanders supporters who say they will not just support Biden out of party loyalty or dislike of Trump.

Those who backed Sanders were especially fond of Sanders' progressive policies such as Medicare for all, which Biden opposes.

Still, Sanders has encouraged his younger supporter to set aside their policy differences in favor of unifying around Biden.

In turn, Biden appealed directly to those young voters, saying he would do whatever it takes to win their support.

"To your supporters: I see you, I hear you, I understand the urgency of what it is that we have to get done in this country, and I hope you'll join us," Biden said.