Former Secretary of State Hillary Clinton and Sen. Bernie Sanders shake hands before the CNN Democratic presidential debate in April. (Samadjewel Samad/Getty Images)

The Rev. Jesse Jackson gave Bernie Sanders props for not taking his supporters and bolting from the Democratic Party, as the senator from Vermont prepares to endorse Hillary Clinton on Tuesday.

The veteran civil rights activist said he saw parallels to his own insurgent campaign in 1988 in Sanders’s run this cycle, when the little-known independent became the big story in the Democratic primary season with his strong performance against party heavyweight Clinton.

“What I chose to do was expand the Democratic Party, even though it did so kicking and screaming, rather than start a new party. Bernie made the same decision. Expand the party rather than split it,” Jackson said. His campaigns, in 1984 and 1988, were credited with registering millions of new voters, especially minorities and young people.

Jackson won 7 million votes in 13 primaries and caucuses in 1988, which earned him 1,200 delegates. Like Sanders, Jackson did not immediately concede and endorse presumptive nominee Michael Dukakis. Instead, he negotiated for the inclusion of certain issues in the platform, changes to party rules and recognition at the convention. The two sides were still wrangling over such matters, including whether Jackson would be considered for vice president, when the convention began. Jackson ended up backing and campaigning for Dukakis, but the Democrats lost the White House that year to George H.W. Bush.

He said the issues that his campaign raised in those campaigns are “now consistent with the high principles of the party.” But at the time, ideas such as reestablishing relations with Cuba and pursuing a two-state strategy for Israel and the Palestinians were not embraced. He said he also fought for proportional allocation of pledged delegates, as opposed to a winner-take-all system — a rule that worked for himself in 1988, then-candidate Barack Obama in 2008 and Sanders this year.

“The first time around, I added 2 million new voters and had only 400 delegates,” he said, referring to his 1984 campaign. “When we got proportionality my delegate count went up to 1,200 delegates.”

Clinton won the delegate battle with 2,811 pledged delegates and superdelegates. Sanders got 1,879 delegates, according to the Associated Press. To win the nomination, a candidate needs 2,383 delegates.

Jackson said Sanders had to “negotiate for the interests of his constituency” and force the party to acknowledge their electoral clout.

He said Sanders is to be applauded for having “kept his word” and preparing to back Clinton. “He didn’t fall for the bait of starting a third party, which he could have done. He operated as a statesman.”