June 11 (Bloomberg) -- This year’s U.S. presidential race is considered a tossup by both sides, and unforeseen events could prove determinative: contagion from the European economic crisis, war or terrorism.
The largest imponderable is the economy. With a Republican- controlled House of Representatives that isn’t eager to help a Democratic president in an election year, even a mild stimulus is a non-starter. Any small impetus provided by Chairman Ben Bernanke’s Federal Reserve is beyond the control of politicians.

There are some foreseeable milestones, however, that will also help shape the outcome of the Nov. 6 presidential election. These include:
June 28: Give or take a few days, this is when the Supreme Court hands down its decision on President Barack Obama’s health-care law. More than a few Republicans see this as a win- win situation. If the measure is retained, the Republican base will be energized for the general election; if it isn’t, Obama’s signature first-term achievement will be undercut.
If the law is upheld, the campaign will stress the law’s unpopular positions and the need to “vote in November to change that,” says Ed Gillespie, a senior adviser to the likely Republican presidential nominee, Mitt Romney.
Wasted Years
“If it goes out the window, people will feel like we’ve wasted two years we didn’t have to waste when the president should have been more focused on job creation and the economy,” Gillespie says.
Obama strategists are less upbeat and more nuanced. If the law is upheld, they plan to stress its popular elements, a challenge they’ve failed to meet for the past two years. If it’s overturned, there will be a temptation to attack both the court’s decision as driven by ideology and to put Romney on the spot as to what he would do.
“There are grounds, polling shows, to take on the decision; people think this is an exceptionally political court,” says Geoff Garin, a Democratic pollster. “And there will be a downside for Romney. It begs the question of what he would do next. He really doesn’t have any answers.”
This month, the high court also is expected to rule on Arizona’s anti-immigration law. The politics here may slightly favor the Democrats: If the measure is upheld, the court’s decision will energize Hispanic voters who are likely to vote overwhelmingly for Obama.
Aug. 27-30: The Republican National Convention will help set the tone for the general election. Successful conventions, such as 1988 for Republicans and 1992 for Democrats, launched winning candidates. Conversely, messy conventions -- the Democrats’ in 1980 or the Republicans’ in 1992 -- proved impossible to overcome.
In Tampa this year, the Republicans will bash Obama as a failed president who is in over his head. They’ll also try to shed their image as a narrow club of rich guys by trotting out struggling Americans with whom to empathize and by highlighting more diversity than commonly seen at Republican gatherings.
On the last night, in his acceptance speech, the nominee has two challenges. He needs to show he’s plausible, not scary; that should be easy. The other is to offer a credible, hopefully inspiring vision to the country; that’ll be hard.