John Judis makes  a good observation in his article on Romney’s foreign policy:
Some cynics argue that you should ignore what a presidential candidate says about foreign policy. But this analysis makes a rule out of exceptions. Over the last four decades, presidents have generally attempted to do what they said they would. It is only when they have encountered impediments that they have changed course.
This is mostly correct, but it also overstates the degree to which even the “changed” courses represent major changes from what the candidates pledged to do. Everyone remembers Bush’s “humble foreign policy” line, but fewer seem to remember that he campaigned on missile defense and criticized Clinton’s preference for working through international institutions. When he withdrew the U.S. from the ABM Treaty, that was something that should have been expected. Likewise, it should have come as no shock later when Bush was willing to ignore international institutions and international law as he saw fit. As a candidate, Bush promoted the idea of cultivating a relationship with India, and strengthening ties with India was one of the few constructive legacies Bush left behind.
The administration’s fixation on Iraq was there before the 9/11 attacks, and the attacks created the political atmosphere at home that allowed them to act on that fixation. It is easy to contrast Bush’s aversion to nation-building with the nation-building projects that the U.S. undertook in Afghanistan and Iraq, but this overlooks how ill-prepared and unenthusiastic for these projects the administration actually was. Planning for post-invasion Iraq was so minimal and poor in large part because there was an expectation that it was unnecessary. The substance and goals of Bush’s foreign policy didn’t change that much.
It is equally easy to cite Clinton’s campaign criticism that Bush was “coddling dictators” in Beijing as an example of rhetoric that didn’t translate into policy, which ignores the fact that Clinton did govern as a hawkish “New Democrat” the rest of the time. Based on the evidence we have, we have to assume that Romney would govern as the aggressive, hawkish nationalist that he has said he would be. This is a politician who is well-known for yielding to pressure from inside his party, and he famously lacks strong convictions, both of which suggest that he would continue to serve as a vehicle for the ideas of the hawks in his campaign and the rest of his party.