Per The Nation, Bernie supported Jesse Jackson in the 1988 presidential primary race.

[femmocrat]

20. I voted for him in the PA primary.

Jackson did very well in the primaries that year:

In the Super Tuesday races, Dukakis won six primaries, to Gore's five, Jesse Jackson five and Gephardt one, with Gore and Jackson splitting the Southern states. The next week, Simon won Illinois with Jesse Jackson finishing second. 1988 remains the race with the most candidates winning primaries since the McGovern reforms of 1971. Jackson captured 6.9 million votes and won 11 contests: seven primaries (Alabama, the District of Columbia, Georgia, Louisiana, Mississippi, Puerto Rico and Virginia) and four caucuses (Delaware, Michigan, South Carolina and Vermont). Jackson also scored March victories in Alaska's caucuses and Texas's local conventions, despite losing the Texas primary. Briefly, after he won 55% of the vote in the Michigan Democratic caucus he had more pledged delegates than all the other candidates.

However, Jackson's campaign suffered a significant setback less than two weeks later when he was defeated handily in the Wisconsin primary by Michael Dukakis. Dukakis's win in New York and then in Pennsylvania effectively ended Jackson's hopes for the nomination.

http://en.wikipedia.org/wiki/United_States_presidential_election,_1988