Sen. Dick Durbin (Brian Jackson/Chicago Sun-Times via AP)

Sen. Dick Durbin (Ill.), the second-ranking Democrat in the Senate and an early and enthusiastic supporter of Barack Obama's 2008 presidential campaign, is officially throwing his support behind Hillary Rodham Clinton's prospective 2016 presidential campaign.

Durbin, along with Chicago Mayor Rahm Emanuel (D) and Illinois Attorney General Lisa Madigan (D), will headline a high-dollar fundraiser next month for Ready for Hillary, the pro-Clinton super PAC organizing grass-roots support for Clinton's potential candidacy. The three political heavyweights are billed as the "special guests" at a June 5 evening reception in Chicago co-hosted by an array of major Obama donors, according to a copy of the invitation obtained by The Washington Post.

The event underscores the early and full embrace of Clinton from key figures in Obama's political organization, even as Vice President Biden contemplates a presidential run of his own in 2016. Senior Obama staffers — including Jim Messina, Mitch Stewart and Jeremy Bird — are advising super PACs clearing the way for Clinton, while Sens. Tim Kaine (D-Va.) and Claire McCaskill (D-Mo.), both early Obama backers in the 2008 race, have signed up with Ready for Hillary. Last fall, Sen. Charles E. Schumer (N.Y.), the No. 3 Democrat in the Senate, endorsed Clinton and declared, "Run, Hillary, Run!" during a visit to Iowa.

Durbin played a leading role in Obama's campaign from day one, as the young senator battled Clinton in the 2008 Democratic primaries. Emanuel, a former White House political adviser to President Bill Clinton and White House chief of staff to Obama, announced  this month that he would endorse Clinton in 2016. And Madigan, who has been close to Obama since they served together in the Illinois state legislature, is considered a rising star in the state.

Tickets to the Chicago reception, to be held at Phil Stefani's 437 Rush, a steakhouse just off the Magnificent Mile, are $1,000 per person, making it one of Ready for Hillary's biggest fundraising events. The group regularly holds grass-roots fundraisers around the country where tickets go for $20.16.

Among the co-hosts are Laura Ricketts, a co-owner of the Chicago Cubs and a major bundler for Obama's campaigns. Her father, Ameritrade founder Joseph Ricketts, is a significant Republican donor, while her brother, Peter Ricketts, won the GOP nomination for governor in Nebraska last week. 

Others on the host committee include Alan and Andrea Solow, Obama bundlers and prominent national Jewish leaders; Kevin Conlon, a top Chicag0-based political strategist and Obama fundraiser; Wendy Abrams, a leading environmental activist; Lou and Susan Manilow, prominent arts philanthropists and Democratic donors; Niranjan Shah, a Democratic donor who runs an architectural firm; Lynn Cutler, a former Clinton White House aide; and Bernadette Keller, the wife of William M. Daley, a prominent Chicago political figure who served as White House chief of staff to Obama and as secretary of commerce under Clinton.