The Chicago Teachers Union, or CTU, showed a keen sense of timing by going on strike yesterday. All the stars were in alignment for the union: a strike in Obama's adopted hometown, against his former top aide, in September of his re-election year. The teachers thus gain maximum leverage against the White House and have an excellent chance of forcing a resolution in their favor. Their small war against Mayor and former White House Chief of Staff Rahm Emanuel disrupts Democratic unity at a critical time and marginally disrupts union-led efforts on Obama's behalf in nearby states like Wisconsin and Iowa.

But if the strike is good for the teachers, it's also good for Republicans: It brings back to the forefront the same political issues that Wisconsinites have been dealing with over the last two years. And it highlights, once again, the dangers of exempting large groups of government employees from the legislative process through monopoly collective bargaining agreements.

Most public expenditures are decided through legislation and the democratic process, but not monopoly collective bargaining agreements for public employees. Systems that allow them give government employee unions an inordinate incentive to throw their political weight around because the unions understand they can help choose their own adversary across the negotiating table.

After Wisconsin's Republican governor, Scott Walker, removed wages and benefits as subjects of collective bargaining for teachers and most other public employees, public employee unions rebelled throughout 2011 and 2012. They spent millions, but they never managed to win the public's sympathy for their cause -- in part because Wisconsin's public employees draw higher salaries and contribute less to their own benefits than their private-sector counterparts. Over two years, the unions lost three successive elections that focused on their bargaining rights.

If the unions in Wisconsin are unsympathetic characters, then the CTU is much more so. For years, the union fought tooth and nail to maintain one of the shortest school days in America -- 5 hours and 30 minutes. In 2003, when CTU President Deborah Lynch agreed to a 15-minute increase in the school day in exchange for a seven-day reduction in the school year (a net 5 extra hours of class time per year), it cost her re-election. Mayor Emanuel's current demand for a 7-hour school day has been one of the many flash points in the current broken-down negotiations. But the biggest sticking point is his plan to get rid of the worst-performing teachers in the system.

CTU teachers are paid well. A first-year teacher straight out of college makes more than $50,000 in salary and pensions for teaching less than 39 weeks out of the year. Experienced teachers with advanced degrees and grad school credit can make six figures if they work 43 weeks. Such high compensation proves that Chicago teachers are hardly exploited peons. Bear in mind, as they shut children out of schools this week, that they just rejected a 16 percent pay raise over four years, at a time when most working Americans are happy just to have a job.

The White House refuses to take a position on the strike -- for now. But Obama might have to apply pressure for a solution if it drags on. The union, one of Obama's first endorsers in his 2008 run, has the president right where it wants him. He can throw Emanuel under the bus quickly, or else watch his union supporters drag their unpopular cause into this year's election. Imagine the irony if Obama is wounded this fall by his best union allies.