Most of the polls you see in the presidential campaign are national polls. That's as it should be. This is a national campaign, and the winner will be president of the whole nation.

But the campaigns themselves don't much care about national polls. They're focused on 8-12 battleground states. That's pretty much all they care about. And they have a lot of information on what's going on in those states. They're looking at not just polls, but registration numbers, volunteer information -- anything that can give them a sense of what will swing Ohio.

Most of that information is private. But NBC's First Read -- you're subscribed to that, right? -- has a helpful breakdown of what the polls are telling us. They break it down like this:

Solid Dem (no chance at flip): DC, DE, HI, ME (3 EVs) MD, MA, NY, RI, VT (70 electoral votes)
Likely Dem (takes a landslide to flip): CA, CT, IL, WA (94)
Lean Dem: ME (1 EV) MI, MN, NJ, NM, OR, PA (73)
Toss-up: CO, FL, IA, NV, NH, NC, OH, VA, WI (110)
Lean GOP: AZ, GA, IN, MO, NE (I EV) (49)
Likely GOP (takes a landslide to flip): AL, LA, MS, MT, ND, SC, SD, TX (79)
Solid GOP (no chance at flip): AK, AR, ID, KS, KY, NE (4 EVs) OK, TN, UT, WV, WY (63)

What's that? You want to see that in graph form? Fine.

Zeroing in on the toss-up column, they list the swing states from most likely to flip to Romney to least likely to flip to Romney:

1. North Carolina
2. Iowa
3. Florida
4. Colorado
5. Virginia
6. Nevada
7. Ohio
8. Wisconsin
9. New Hampshire

Their conclusion:

What’s striking about this list is if you give Romney the Top 4 (NC, IA, FL, and CO) that only gets him to 250 electoral votes. And if you give him the next two on the list (VA and NV), he’s still one short of 270 (bringing us to that 269-269 tie). That means he has to put one of Ohio, Wisconsin, or New Hampshire into the mix to get past 270. Bottom line: Romney’s map to 270 is more than doable, but it’s also a high-wire act.

NBC's analysis backs up something I'm hearing, too. In a close race, Ohio is Obama's firewall. For reasons no one quite understands -- though everyone has their theories -- Romney has had real trouble gaining traction there. That might change. There's some evidence, actually, that it is changing. But without Ohio, Romney's got a very difficult road to 270.

Bottom line? If you limited me to one data point to use in predicting the election, I'd use a national poll. If you gave me two, I'd add a poll of Ohio.