Who wins when foreign policy becomes campaign focus?

When foreign policy crises intrude into presidential elections, they have the ability to shake up campaigns and force candidates to adjust their plans, writes Prof. Julian Zelizer, a professor of history and public affairs at Princeton University, on CNN's Opinion page.

Zelizer looks at when it has helped the incumbent, like Republican Dwight Eisenhower, and when it has hurt the sitting president running for re-election, as was the case with Jimmy Carter.

What will happen if the current crises continue or get even worse:

For President Obama the risks are very clear. If the situation deteriorates, these hot spots will offer the GOP evidence that the president is not an effective leader. Republicans will argue that this proves all the talk about the successes of his foreign policy record is overblown. The danger is particularly acute with Libya and Egypt, two countries that have been described as relative success stories in the Obama era of foreign policy since autocratic leaders were overthrown. These crises will also force the president to devote more attention to working in the Oval Office rather than spending time on the campaign trail.

The risks are also great for Mitt Romney. The crises could easily benefit Obama just as they did Eisenhower.

Anything having to do with overseas issues takes attention away from the economy, the area where Obama is most vulnerable.

Read Zelizer's analysis here.