In American politics, what's supposed to happen, tends to happen. Mitt Romney is now our nominee, just as he should be. Republicans nominate the second-place finisher from the previous nomination contest.

Rick Santorum made it interesting for a while, but there was always destined to be a challenger to the front runner. Santorum was something of a surprise, but he charged and he lost according to script.

Probably the only time Romney was in real danger was when Rick Perry was briefly gathering steam. But a unique feature of the 2012 GOP nominating process saved Romney. The GOP had an unprecedented number of debates, and these killed Perry. Romney didn't beat Perry; Perry went into debates unprepared and almost immediately imploded. In a more traditional campaign he could have raised the money, limited his unscripted exposure, rallied the anybody-but-Obama voters and maybe beat Romney. But it was not to be. What is supposed to happen has now happened.

Now, as a viewer's guide, there will be roughly four remaining eras of the 2012 campaign.

The first will be a Romney re-introduction and his only honeymoon. This era will be short. Romney will get a fresh look and flattering profiles. He is the winner, and unless he commits a gaffe, it will last through the Sunday talk shows on April 22. The Obama campaign should be mostly quiet during this era. Let Romney have his moment and remember, as Lee Atwater said, in politics, “Never kick a man when he is up.”

The next period will be from late April until the Fourth of July. This era will mostly be about fundraising and organization-building, punctuated by the campaigns swapping blows in public and with ads in battleground states. But not much should happen.

Next you will have the summer doldrums from July 4th until the conventions. This will be a time when even insiders will be distracted, and the campaigns will be bothersome or just invisible to voters on vacation and enjoying their summer.

Then we will have the conventions and the Labor Day launch of the general election. This will last until mid-October. It is where much of the real action will occur. Republicans will have their ticket and every day will count. The ads, the debates and the messages will all be sharply focused.

Last, the final act, from Oct. 15 until Election Day, will be the intense period when undecideds decide if they are going to vote and for whom. Campaigns often forget how late many voters make their decisions. This era will consist of the political equivalent of hand-to-hand-combat and a few surprises, including the likelihood that a prominent Northeast newspaper and one of the three traditional broadcast TV networks will unload an October surprise on the Republican nominee. An alleged affair, scandal or retread of old rumors will be revealed with much drama and gasping from the insiders. Voters may or may not react at all.

And, of course, it all leads to Election Day. If you had to bet, remembering that in American politics what is supposed to happen, tends to happen, you would bet on Obama. But his odds are no better than 52/48. Interesting.