SAN FRANCISCO >> President Barack Obama and the Rev. Al Green on tour?

Obama was joined by the soul singer at a Democratic fundraiser on Thursday, a month after the president launched into a brief, impromptu version of Green’s "Let’s Stay Together" at New York’s Apollo Theater.

Obama thanked Green, prompting a member of the audience to shout, "Give us a verse!" The president declined to sing this time, telling about 70 campaign donors that he "took a chance at the Apollo and I’m not going to take a chance again."

"After re-election I might go on tour with the good reverend — be his opening act," Obama said.

But he warned, "I don’t want to lose any further votes because of my singing voice."

Obama’s crooning of "Let’s Stay Together," starting with the vibrato "I” and finishing up with the line "so in love with you," quickly went viral on the Internet following the New York City fundraiser. His campaign released a ring tone of the president’s turn as a soul singer.

Prior to the president’s remarks on Thursday, Green was overheard singing his classic song at the fundraiser in San Francisco’s Pacific Heights neighborhood.