If past is prologue, former Massachusetts governor Mitt Romney should win the Illinois presidential primary on Tuesday.

Republican presidential candidate and former Massachusetts Governor Mitt Romney greets diners at a restaurant during a campaign stop in Rosemont, Illinois March 16, 2012. REUTERS/Jim Young

It’s because of money.

But, wait, you argue. Romney has outspent Santorum in every single caucus and primary. And money hasn’t equaled certain success for Romney in lots of places — including Alabama and Mississippi earlier this week.

That’s true. But it amounts to an overly simplistic reading of how Romney’s financial advantage plays itself out on a state-by-state basis.

In order to grasp why Romney’s financial edge matters more in Illinois than in Alabama or Mississippi, you need to understand that the primary states fit relatively neatly into two basic categories: retail states and TV states.

Retail states tend to be smaller (population-wise) and, as a result of their size, voters have an expectation of seeing a candidate show and prove their quality on the campaign trail. These are states where it’s not entirely unreasonable to expect that you might be able to meet the candidates asking for your vote in a presidential race. They also tend to be states with one (or at most two) dominant media markets, meaning that if a candidate does an event in a big city in the state, he (or she) will get near-statewide exposure on the news that night.

States that have voted so far in the Republican presidential race that fit this model: Iowa, New Hampshire, South Carolina, Alabama and Mississippi (among others).

TV states are large population states where the only way most voters ever get to know a candidate is through ads. Retail politicking is largely pointless in these places; no candidate can hope to meet even a tenth of the people he needs to vote for him to win.

The TV states that have voted so far in the presidential primaries: Florida, Ohio and Michigan.

It doesn’t take a genius to notice that Romney tends to win TV states and lose retail states. (New Hampshire is the outlier but Romney’s geographic connection from being the governor of Massachusetts explains his success in that retail state.)

There are two reasons for that phenomenon.

First, Romney is, at best, an awkward presence on the campaign trail. He’s uncomfortable with the sort of close-quarters stumping that retail states demand. And voters pick up on that.

Second and more importantly, Romney’s spending edge is more impactful in a TV state where there are lots and lots of media markets and in which what happens in one part of the state doesn’t even get covered in other parts of the state. Take Florida. The Panhandle of the state and the Miami-Dade area have almost nothing — culturally or politically — in common. Romney could target TV messages to both types of voters in a way that Santorum or former House Speaker Newt Gingich just can’t. Money matters more in TV states than it does in retail ones.

Which brings us to Illinois where Romney and the super PAC supporting him are set to drastically outspend Santorum and his affiliated super PAC.

According to media buy information provided to the Fix on Thursday night, Restore Our Future, the super PAC supporting Romney, has already spent $2.4 million on television ads over the past two weeks in Illinois. Romney is spending another $1.1 million this week.

Compare that to Santorum who is spending $207,000 on ads in Illinois this week and the Red White & Blue Fund, Santorum’s super PAC, which is dropping $310,000 on television ads.

Total spending in Illinois (for you non-math majors out there): Romney and Restore Our Future $3.5 million, Santorum and Red White & Blue Fund $517,000. That’s roughly a seven-to-one edge.

Those spending numbers should be determinative for Romney in a TV state like Illinois. If they aren’t, he could have bigger problems on his hands.