During the primetime speeches last night by Ann Romney and Chris Christie, something peculiar did not happen. Barack Obama’s name was not mentioned. Why?

At first blush, it might seem like an odd move. After all, this president is unpopular and in a weakened political position. Isn’t the time to strike now? The answer is, probably not.

For months, Democratic politicians, pundits, and strategists have been insisting that this election would be a choice, not a referendum. Little did they know that the Republican party actually agreed with them. Democrats thought that this “choice, not referendum” meme was their trump card, but in fact virtually every successful challenger throughout American history has won by making the contest a choice.

One theme that connects the political victories of Barack Obama in 2008, George W. Bush in 2000, Bill Clinton in 1992, Ronald Reagan in 1980, Jimmy Carter in 1976, and all the way back to Thomas Jefferson in 1800 is a simple, powerful message: The other side has failed America, but we can do better.

If you look at the polling data, you can see pretty clearly that a Republican convention that focuses on the failures of Barack Obama would be tantamount to beating a dead horse.

Without doubt, this president has consolidated the core Democratic vote. Given the political and economic challenges he has faced, this is no small feat. Even so, it amounts to only about 47 percent of the public, maybe a little less of the voting public. He has, naturally, lost the 45 percent or so of the public that makes up the core Republican coalition, which leaves about 8 to 10 percent in the middle that is truly up for grabs.

Poll after poll has shown that these people generally do not approve of the job this president has done; and on the economy, the deficit, and the health care bill, his numbers are even worse. Importantly, he has been “under water” – below the magic line of 50 percent – with these voters for years. Indeed, the last time the Gallup poll found the president’s job approval with “pure independents” at or above 50 percent was June 2009.

So, the president has managed to make the case against himself. The middle of the country is deeply disappointed in the job this president has done, and that has been the case basically for three years. What is left for the GOP ticket to do is to make the positive case for change. That is what we began to see last night.

It would be the height of political malpractice to fall into the false dichotomy the Democrats have been preaching – a “choice” versus a “referendum.” Every election is in fact both. First, it is a referendum on the incumbent: if he has done a good job, he gets reelected without much consideration of the challenger. But if he has not done a good job, then the public is going to take a close, careful look at the fellow who presumes he can do better, to see if there’s any steak to the sizzle.

That is the crux of the 2012 election, which means it is up to the Romney-Ryan campaign not merely to attack the president, but to present a positive case for itself. Indeed, this is the number one priority.

So tonight, we should expect more of the same. Though President Obama will likely be mentioned by name, it will be in the context of: “He’s failed. We can do better, and here’s why.”

That’s how challengers beat incumbent parties, going all the way back to the first transition of power in 1800. Last night, the Romney campaign demonstrated that they understand this, which means Team Obama should be very worried.