President Barack Obama stumped for Alexi Giannoulias, the Democrat vying this November for Obama’s former Senate seat, on Thursday evening in Chicago.

The fundraiser at the Drake Hotel and a dinner for Giannoulias later in the evening at a private Chicago residence were expected to raise up to $800,000, which was to be split between the Senate candidate’s campaign and the Democratic Senatorial Campaign Committee, according to pool reports.

Giannoulias introduced Obama to the crowd of about 400 as “my friend, my mentor, one of the greatest fighters I’ve ever encountered.”

The president returned the compliment and encouraged the crowd to get out and vote. “Alexi is my friend. I know his character. I know how much he loves this country. I know how committed he is to public service,” he said.

Giannoulias is running against GOP Rep. Mark Kirk for the seat being vacated by Democratic Sen. Roland Burris, who was appointed to replace Obama.

Obama also cracked a joke about Rahm Emanuel, who stepped down last week as his chief of staff to run for mayor of Chicago. “This is Chicago. Politics is sport here. By the way, have you seen my chief of staff? I was like looking around and was like, what happened?” he said, drawing laughs from the crowd.

CNN reported Thursday that Obama is planning a major campaign swing this month to aid three vulnerable Senate incumbents: Patty Murray of Washington, Barbara Boxer of California and Majority Leader Harry Reid of Nevada.

He will be in Seattle on Oct. 20 for Murray, in San Francisco on Oct. 21 for Boxer and in Las Vegas on Oct. 22 for Reid, CNN reported, citing senior Democratic officials.