(CNN) -- As Mitt Romney prepares to make the case for a first term, give a thought to what we can expect from a Barack Obama second term. It's probably going to look a lot like the second terms of George W. Bush, Bill Clinton, Ronald Reagan, and Richard Nixon -- driven not by his own agenda, but by events beyond his control. Bush's second term was defined by the after-effects of the Iraq decision he made in his first term; Clinton's by impeachment and the Internet boom; Reagan's by deficits and Gorbachev; Nixon's by Watergate. And what will define Obama's?
@highlight
David Frum: A second term for Barack Obama would have a different shape
@highlight
He says Dems likely won't control both houses, giving him little chance for major legislation
@highlight
Frum: Obama would likely benefit from an improving economy but would face challenges overseas
@highlight
U.S. energy production boom would bring U.S. closer to energy independence, he says
The @placeholder tax cuts of 2001, extended in 2010, will expire at the end of 2012.