CHARLOTTE, NC -- The Republican convention last week in Florida and the Democrat convention that wrapped up here Thursday both went off without a hitch.

Well, except for a hurricane, a last-minute stadium change, thunderstorms, a shortage of balloons for President Barack Obama, boos for Israel and Clint Eastwood's now infamous speech to an empty chair.

But at least there were no locusts, and so the  presidential election is finally and officially underway, which for many Americans in the dozen or so swing states that actually matter -- Ohio, Florida, Virginia, Colorado, and Iowa among them -- means hundreds of millions of dollars in more negative attack ads.

But what the two conventions -- neither contested and both heavily choreographed from start to finish -- did make crystal clear is that November's election is a battle for the middle-class vote.

Yes, the GOP trotted out their Hispanic, female and young leaders to show they aren't an old white boys' club, and yes, Democrats revelled at riling up the left over Republicans' social conservativism.

But the central theme of both fetes was not abortion rights, gay marriage or immigration.

As Bill "Bubba" Clinton quipped in 1992, "it's the economy, stupid."

Republican Mitt Romney has promised, if elected, lower taxes for all -- including the ultra-rich -- and to get government out of the way to unleash economic growth he says is being hampered by burdensome regulations on businesses big and small.

For Democrats, Americans are all in this economic recovery together and the government does have a role to fulfil levelling the playing field and investing in the foundations of society -- roads, the social safety net, education and health care.

Over the next two months, the middle class will have to decide who they believe.

This week, the US debt topped $16 trillion, adding what is perhaps the world's most expensive monkey wrench into the campaign. The presidential election is Nov. 6.