(Updated 10:50 p.m., Sat., June 7)

Seven years after leaving the Republican Party, Missouri Attorney General Chris Koster has in effect taken the reins of the Missouri Democratic Party.

That point was underscored Saturday night when -- shortly before the Democrats' annual Jefferson-Jackson dinner -- Koster presented the state party chairman a check for $100,000.

That's the second such six-figure donation that Koster has given the state Democratic operation in the past year -- making him the largest single donor to the state party.

"It's a testament to his leadership and his commitment to bring about progressive leadership in Missouri,'' said party chairman Roy Temple in a brief interview before the dinner.

Koster, who is running for Missouri governor in 2016, told St. Louis Public Radio that he expects the money to be used primarily to help Democratic candidates for the state House and state Senate, where the party currently is heavily outnumbered by Republicans.

His contribution also is intended to reinforce "the concept of unity within the party," which Koster said has improved within the past year.

While he didn't mention it, Koster's generous help also appears aimed at bolstering his acceptance by veteran Democrats, some of whom long had been wary of his 2007 party switch -- just a year before he won the Democratic nomination for Missouri attorney general.

But Saturday night, the crowd of roughly 500 gathered at the Renaissance Grand hotel gave Koster a standing ovation as he took to the stage. Koster, in turn, noted in his speech that he had headlined 15 fundraising events since last year for Democratic legislative candidates.

McCaskill, Nixon miss dinner

Outside the ballroom, a huge sign focused on Koster and his achievements. Another poster listed Koster, U.S. Sen. Claire McCaskill and Ameren as the biggest donors for the Jefferson-Jackson dinner, the state party's largest fundraising event.

Aside from the money, Koster also was the highest-ranking state Democrat at the dinner. McCaskill, D-Mo. -- also influential in party operations -- was with her husband, who had just been released from a Washington hospital after becoming ill last week.

Missouri Gov. Jay Nixon, who is the titular head of the state Democratic Party and would traditionally host the Jefferson-Jackson dinner, spent Saturday in Branson. He participated in a PGA golf tournament sponsored by the state and then spoke Saturday night at the Missouri Broadcasters Hall of Fame banquet, a Nixon spokesman said.

Bill Greenblatt/UPI

As a result, it fell to Koster to introduce the dinner's keynote speaker, U.S. Sen. Dick Durbin, D-Ill.

Durbin emphasized the need for Democrats to defend their principles. In particular, he cited the Affordable Care Act -- also known as "Obamacare'' -- which has been a prime Republican target ever since the health insurance law was passed in 2010.

Durbin said he couldn't understand why Republicans were so against expanding Medicaid, and opposed to the health insurance exchanges, which he emphasized have made it possible for millions of uninsured Americans to get coverage.

"I'm not backing down, I'm not apologizing, I'm proud of that vote,'' Durbin said.

Koster and the two other statewide Democratic officials at the dinner -- state Treasurer Clint Zweifel and Secretary of State Jason Kander -- also reinforced their support for expanding Medicaid, which the GOP-controlled General Assembly has declined to approve. Nixon and others said the expansion would add about 300,000 low-income working Missourians to the Medicaid rolls.

Koster predicted that legislators will eventually approve the expansion, as more Missourians -- including conservatives -- press for the coverage and the $2 billion a year in federal Medicaid dollars that the state is now declining to receive. He called it “a battle that we will unquestionably win in this state; the only question is when.”

Democrats pledge continued support for gay rights

Koster also touched on several social issues that he said in 2007 were the reasons he was leaving the GOP.

Koster noted that the General Assembly has yet to pass a bill to protect people from losing their jobs because of their sexual orientation. "Missourians should never be denied a place to live or a job simply because they are gay,” he said.

And he called for his former party to remove anti-gay language from the national GOP platform.

But of Saturday night's speakers, Kander arguably offered the sharpest condemnation of Missouri's Republican lawmakers, asserting, "I don't know how you go home from Jefferson City thinking you've done a good job when you've denied health-care coverage to 300,000 people."

Kander also told the crowd, "You might be under the impression that things are terrible in Jefferson City. You're right."

Jo Mannies/St. Louis Public Radio

For all the lament about Democrats' low numbers in the General Assembly, many Democrats in the ballroom acknowledged that this fall's elections may not improve Democratic fortunes. Said Doug Brooks, one of Missouri's members on the National Democratic Committee: "Our mood with regard to the legislature is grim."

Still, most of the speakers noted that Democrats now hold four of Missouri's six statewide offices. And Durbin highlighted McCaskill's surprisingly strong re-election in 2012, which helped the entire Democratic ticket, as a result of missteps by her Republican rival, former U.S. Rep. Todd Akin.

But it fell to a former Missouri officeholder -- former U.S. Sen. Jean Carnahan -- to offer the evening's strongest words of encouragement to fellow Democrats worried about their party's standing now and after the fall elections. Carnahan received the state party's lifetime achievement award.

Carnahan, who lost her seat during a 2002 national GOP wave, recalled the inspirational 2008 race of college track star Heather Dorniden, who fell during the contest but got back up and went on to win anyway.

"Democrats have tripped and fallen in many elections,'' Carnahan declared, but still manage to come back victorious.