Colorado or Iowa. If he doesn't, he loses.

Extremely unlikely.

Assuming Obama wins PA & MN (heavily favored to do so), Romney has three possible winning combinations:
http://www.270towin.com/presidential_map/combinations.php?party=Republican&num_rem=79&st_remain=FL,OH,NC,WI,CO,IA,NV&me=&ne=

He must win FL, OH & NC plus 2 or 3 other battleground states

As stated above, it's very unlikely.

keep it handy on election night! Plug in each state as Obama wins and it will give you the EV count each time.

For Obama to win he needs:

http://apps.npr.org/swing-state-scorecard/

2 states
I Florida (29) + i Ohio (18) = 284I Florida (29) + s Virginia (13) = 279I Florida (29) + v Wisconsin (10) = 276I Florida (29) + F Colorado (9) = 275I Florida (29) + L Iowa (6) = 272I Florida (29) + g Nevada (6) = 272

I Florida (29) + d New Hampshire (4) = 270

3 states
i Ohio (18) + s Virginia (13) + v Wisconsin (10) = 278i Ohio (18) + s Virginia (13) + F Colorado (9) = 277

i Ohio (18) + s Virginia (13) + L Iowa (6) = 274i Ohio (18) + s Virginia (13) + g Nevada (6) = 274i Ohio (18) + s Virginia (13) + d New Hampshire (4) = 272

i Ohio (18) + v Wisconsin (10) + F Colorado (9) = 274i Ohio (18) + v Wisconsin (10) + L Iowa (6) = 271

i Ohio (18) + v Wisconsin (10) + g Nevada (6) = 271i Ohio (18) + F Colorado (9) + L Iowa (6) = 270

i Ohio (18) + F Colorado (9) + g Nevada (6) = 270

4 states
i Ohio (18) + L Iowa (6) + g Nevada (6) + d New Hampshire (4) = 271s Virginia (13) + v Wisconsin (10) + F Colorado (9) + L Iowa (6) = 275

s Virginia (13) + v Wisconsin (10) + F Colorado (9) + g Nevada (6) = 275s Virginia (13) + v Wisconsin (10) + F Colorado (9) + d New Hampshire (4) = 273

s Virginia (13) + v Wisconsin (10) + L Iowa (6) + g Nevada (6) = 272s Virginia (13) + v Wisconsin (10) + L Iowa (6) + d New Hampshire (4) = 270

s Virginia (13) + v Wisconsin (10) + g Nevada (6) + d New Hampshire (4) = 270s Virginia (13) + F Colorado (9) + L Iowa (6) + g Nevada (6) = 271

5 states
v Wisconsin (10) + F Colorado (9) + L Iowa (6) + g Nevada (6) + d New Hampshire (4) = 272.



Obama I Fla.29 i Ohio18 s Va.13 v Wis.10 F Colo.9
L Iowa6 g Nev.6 d N.H.4.Ways He Can Win

Romney must win at least 4 tossup states. Possible combinations:

4 states
(back to top)I Florida (29) + i Ohio (18) + s Virginia (13) + v Wisconsin (10) = 276

I Florida (29) + i Ohio (18) + s Virginia (13) + F Colorado (9) = 275I Florida (29) + i Ohio (18) + s Virginia (13) + L Iowa (6) = 272I Florida (29) + i Ohio (18) + s Virginia (13) + g Nevada (6) = 272

I Florida (29) + i Ohio (18) + s Virginia (13) + d New Hampshire (4) = 270I Florida (29) + i Ohio (18) + v Wisconsin (10) + F Colorado (9) = 272

5 states
I Florida (29) + i Ohio (18) + v Wisconsin (10) + L Iowa (6) + g Nevada (6) = 275

I Florida (29) + i Ohio (18) + v Wisconsin (10) + L Iowa (6) + d New Hampshire (4) = 273

I Florida (29) + i Ohio (18) + v Wisconsin (10) + g Nevada (6) + d New Hampshire (4) = 273I Florida (29) + i Ohio (18) + F Colorado (9) + L Iowa (6) + g Nevada (6) = 274

I Florida (29) + i Ohio (18) + F Colorado (9) + L Iowa (6) + d New Hampshire (4) = 272I Florida (29) + i Ohio (18) + F Colorado (9) + g Nevada (6) + d New Hampshire (4) = 272

I Florida (29) + s Virginia (13) + v Wisconsin (10) + F Colorado (9) + L Iowa (6) = 273

I Florida (29) + s Virginia (13) + v Wisconsin (10) + F Colorado (9) + g Nevada (6) = 273I Florida (29) + s Virginia (13) + v Wisconsin (10) + F Colorado (9) + d New Hampshire (4) = 271I Florida (29) + s Virginia (13) + v Wisconsin (10) + L Iowa (6) + g Nevada (6) = 270

6 states
I Florida (29) + s Virginia (13) + F Colorado (9) + L Iowa (6) + g Nevada (6) + d New Hampshire (4) = 273

I Florida (29) + v Wisconsin (10) + F Colorado (9) + L Iowa (6) + g Nevada (6) + d New Hampshire (4) = 270

7+ states
i Ohio (18) + s Virginia (13) + v Wisconsin (10) + F Colorado (9) + L Iowa (6) + g Nevada (6) + d New Hampshire (4) = 272

...assuming both Iowa and Nevada go our way.