Without Sept. 11, 2001, it is doubtful that New York Mayor Rudy Giuliani would have become a national figure and a presidential candidate. And President George W. Bush’s presidency and legacy would have been entirely different in ways we can hardly imagine. Like it or not, big events, including horrible tragedies, change the trajectory of presidential politics. There are a few potential ramifications in the wake of the Boston Marathon bombing.

File photo (Matt Rourke/Associated Press) Vice President Biden (Matt Rourke/Associated Press)

First, you can see how events may elevate Democrats into the ranks of presidential contenders. Does anyone doubt that Massachusetts Gov. Deval Patrick (D) showed calm, command and leadership during a hellish time? With Hillary Clinton on the sidelines, it is not impossible that Patrick’s image may continue to improve. (Indeed compare Boston to Benghazi, Libya, and you have two very different images of crisis management.) A more contemporary Democrat to the left of Clinton might well give her trouble in 2016.

Second, this may alter President Obama’s focus. Frankly, his domestic agenda is a mess. The budget “grand bargain” he’s been talking about for years is unlikely to occur. He lost on guns. He’s not going to get anything done on climate change. If immigration reform passes, Sen. Marco Rubio (R-Fla.) will get the lion’s share of the credit. So why not turn to national security and make his mark in defusing the North Korean and Iranian threats and protecting the homeland? Lots of presidents including Ronald Reagan (arms control) and Bush (the Iraq surge) have saved their second term by rising above domestic political defeats to achieve significant foreign policy wins.

Third, it may shake the GOP out of its semi-isolationist stupor, reminding activists and candidates that the route to national leadership, especially for conservatives, does not veer left. Ridiculing successful intelligence achievements, concocting convoluted scenarios in which the government turns against U.S. citizens and trying to withdraw from a dangerous world all look misguided if not dangerous after the Boston bombings. That doesn’t mean duplicating the Bush agenda; it’s a new world and the Arab Spring should sober us about our ability to cultivate democracies in the Middle East. But it does suggest that those eschewing a robust foreign policy will have a tougher time if the lessons of the Boston bombing are internalized.

Finally, Boston is a reminder that what a candidate looks like on paper does not determine presidential success. (Otherwise, Gov. Rick Perry would have arguably won the nomination in 2012.) Unexpected events and how pols react to these events are much more determinative of how the electorate regards presidential candidates than votes taken five years ago or a change in position on, say, gay marriage. If the voters can’t imagine a presidential candidate in charge during a national emergency or crisis it’ll be hard for voters to entrust the presidency to him or her.