The battle between President Barack Obama and Republican Mitt Romney will be the most expensive presidential contest ever — by a long shot.

There are two main reasons. It's the first time both major-party candidates are declining post-Watergate federal campaign financing — and the spending limits attached. And the proliferation of super PACS is pumping untold millions into the fray on both sides.

So fasten your seat belts and prepare for a howling tempest of broadcast ads, especially if you live in a battleground state.

Obama and Romney were both coming off a week of intensive national fundraising.

Without Democratic primary opposition, Obama had a huge early advantage. But Romneyis starting to catch up as donors begin opening their wallets.