Former Rep. Rahm Emanuel (D-Ill.) is likely to be the next mayor of Chicago. But the question being answered in Tuesday’s election will be whether the former White House chief of staff clears the threshold to avoid a runoff.

The election marks a major shift in Chicago politics. The top job at city hall is open because Mayor Richard M. Daley, who was first elected in 1989, announced in September that he wouldn’t run for re-election. Daley is the son of former Mayor Richard J. Daley.

And there’s no doubt Chicagoans are excited about the race. More than 73,000 people cast their ballots early, triple the number who did so in the 2007 mayoral race. Several thousand people showed up for the mayoral candidates’ final televised debate on Thursday. Emanuel capped off his campaign with a tour of the city’s 50 wards in 50 hours.

The top contenders in the nonpartisan election are all Democrats, and recent polling has shown Emanuel about 30 points ahead of his closest rivals, former school board President Gery Chico, City Clerk Miguel del Valle and former Sen. Carol Moseley Braun. A recent public poll, commissioned by the Chicago Retail Merchants Association and taken Feb. 13, showed Emanuel with 58 percent of the vote, well over the 50 percent threshold required to win the election outright. Chico got 24 percent, del Valle got 10 percent and Moseley Braun got 6 percent. The poll of 2,252 likely voters had a margin of error of about 2 points.

But that’s better than a Chicago Tribune/WGN poll taken earlier in the month that showed Emanuel with 49 percent, Chico with 19 percent, Moseley Braun with 10 percent and del Valle with 8 percent. That survey of 718 registered voters had a margin of error of 3.7 points.

If Emanuel doesn’t clear the 50 percent threshold, he and the runner-up would go to an April runoff. All three of his closest competitors were predicting the need for a runoff in the last days leading up to the election.

Emanuel had to survive layers of legal challenges charging that because of his tenure as White House chief of staff he didn’t meet the city’s one-year residency requirement. On Jan. 27, just after the Chicago Board of Election Commissioners began printing ballots without Emanuel’s name, the Illinois Supreme Court overturned an appeals court ruling that he didn’t meet the requirement.

Emanuel, the former chairman of the Democratic Congressional Campaign Committee, has gotten some help from national Democrats. In a press conference last week President Barack Obama joked that his former top aide didn’t need his help, but the Chicago Sun-Times reported Monday that some senior White House staffers, including Deputy Chief of Staff Alyssa Mastromonaco and Stephanie Cutter, deputy to White House Senior Adviser David Plouffe, had gone to Chicago to help Emanuel. In January, President Bill Clinton campaigned with Emanuel, who was among his senior advisers in the White House.

Democratic Reps. Jan Schakowsky and Mike Quigley, who replaced Emanuel in the House, endorsed the former Congressman. Other endorsements from members of the Illinois delegation broke mostly by race. Rep. Luis Gutierrez (D) enthusiastically endorsed Chico, appearing in a TV ad and at a number of campaign events with him, and Democratic Reps. Bobby Rush and Danny Davis endorsed Moseley Braun.