Speculation is running rampant that Chicago Teachers Union president Karen Lewis will challenge her nemesis, Mayor Rahm Emanuel, and take his job. It has only accelerated now that Cook County Board president Toni Preckwinkle has removed herself from consideration. Lewis reportedly created an unofficial exploratory committee.

A spur to all this is an automated poll commissioned by the Chicago Sun-Times that shows Lewis with an 9-point lead over Emanuel. The poll’s methodology is problematic, but Emanuel has high negatives no matter how you measure them. Dave Weigel of Slate suggests the poll actually underestimates Lewis’s support, adding what seems to me to be an insulting evaluation of the city’s African-American voters:

(Lewis) trailed by only 3 points with white voters, led by 4 points with Hispanics, and led by 18 points with black voters—a margin that might increase if Lewis ran and black voters discovered that she, too, was black.

If Weigel has some evidence that black voters don’t know that Karen Lewis is black, he ought to present it to the rest of the world.

Lewis has serious weaknesses. She would be, almost by definition, a single-issue candidate running against a well-seasoned, if greatly disliked, machine Democrat. And last week’s AFT Convention demonstrated that her pull within her own union has been overestimated.

Nevertheless, voter emotion has carried many a challenger to victory over an entrenched incumbent, and teacher union officers often have electoral success at the local and state legislative level.

They fare less well in statewide or national elections, although the sample size is small. NEA’s new president, Lily Eskelsen Garcia, ran for Congress in 1998 against a very vulnerable one-term incumbent Republican and lost by 10 points. The Alabama Education Association’s powerful executive secretary Paul Hubbert ran for governor in 1990. He lost by four points to the incumbent Republican.

I haven’t researched it recently, but there was a general dearth of national candidates who have ever even been members of a labor union.

It probably wouldn’t be wise to bet on Lewis, but she has a puncher’s chance of toppling Emanuel. If she wins, she would be the first labor union president to hold such a high elected office, since, well, this guy.