Let’s look at three kinds of numbers: campaign fundraising totals, President Obama’s approval rating, and the head-to-head polls between the potential GOP nominees and the president.

This morning I noted that, while the Perry campaign had tossed out some awfully big campaign fundraising numbers, the actual amount may be less impressive than some imagined. There were two kinds of reactions that I got to that news.

Tony Fratto, a former Bush administration official who is now a business and communications consultant, told me, “Playing the expectations game with presidential fundraising numbers is silly — at the end of the day, you look at the number below the bottom line and make a judgment. If it’s a weak number, it’s a weak number. Setting a low bar — like $10 million — isn’t going to fool anyone. You just have to live with it and talk about the future.” He continued, “All that said, Republican presidential fundraising numbers should all be seen in the context of ‘Waiting for Christie.’ Until it’s logistically impossible for Christie to run, a lot of major donors who would otherwise be backing a contender today will stay on the sidelines.” (Given the “He’s running!” and “No he’s not!” hour-by-hour watch, that may be some time.)

Others had a different, harsher reaction. A GOP operative who’s been critical of the Perry campaign tells me, “One of the main arguments Rick Perry’s campaign made for him getting into the presidential race was that he was a fundraising powerhouse with a huge, national Rolodex. In their own words, they boasted of Bush-like fundraising totals and told Texas reporters they amassed $20 million in just three days. They have to deliver on that.”

So on the money front, the numbers matter as an indication of relative strength. But the real challenge is going to be to keep pace with Obama in the general election.

Then there is Obama’s approval rating. He’s at or near a low point in his presidency. In the RealClearPolitics average, he is hovering around 43 percent approval and 50 percent disapproval. It’s very hard to win an election with that profile, no matter how much money you have. So would Obama rather have a billion dollars in campaign money or a 55 percent approval rating? Frankly, he’s not going to get a billion with an approval rating this bad.

Then there is the electability factor. I’ve said (because voters, operatives, office holders and candidates repeat it over and over again) that the Republicans have a single nonnegotiable item in assessing candidates: electability. Right now this may be Mitt Romney’s strongest card. Since mid-August, in virtually every Gallup, Quinnipiac, Washington Post-ABC News, Bloomberg, CNN and other reputable national poll, Romney does better in the head-to-head matchup against Obama than Perry does. On average, Romney does about 5 percent better than Perry. That is significant, and could represent the difference between winning back the White House and having four more years of Obama.

It’s fair to say that, of these three numerical indicators, the head-to-head matchup is the most important number in the Republican primary. It will, in turn, fuel fundraising numbers. And so long as the president remains vulnerable (but within reach of his Republican challengers), that number will loom larger and larger. It is one very critical reason why the GOP candidates should not simply be playing to the base in the primary.