There's nothing the presumptive Republican nominees can do about the attempts to portray them in the worst possible light. (Cue the ad of Granny being thrown out of her wheelchair and over the cliff.) What matters is how they respond.
Why not start with some of the sillier accusations? One is that Romney is running for president to help the rich. Does this make sense? Romney is worth $190 million to $250 million, according to his campaign. He doesn't have to do anything for the rest of his life, and the next 10 generations of Romneys can live in the style they're accustomed to.
As for helping his rich brethren, Romney, like all conservatives, favors letting taxpayers keep more of their own money and decide how to allocate it. It's self-evident that individuals spend their money more efficiently than the government, and stronger growth lifts all boats. It's a compelling argument, if Romney chooses to make it.
The idea that the GOP's goal is to help the rich at the expense of the poor defies logic. The party's ideas on how to help the poor may differ from the Democrats': better education through school choice; creating incentives to work rather than to loaf. But to endure the ordeal of a presidential campaign to help the rich get richer? The rich may earn the lion's share of the income, but they don't control a majority of the votes.
Then there's Medicare. Last weekend, Obama's tweeter-designate posted an image on Twitter with the following text: "Fact: Paul Ryan would end Medicare as we know it by turning it into a voucher program costing seniors up to $6,350 a year more."
The voucher part is true. But Ryan isn't going to end Medicare as we know it; Medicare is going to do that on its own. It has run a deficit since 2008 and will go bust in 2024, according to a 2012 report by its trustees.
Ryan's "Path to Prosperity" would, starting in 2023, offer senior citizens a choice when they become eligible for Medicare: remain in the current program, or receive premium support for private insurance. Sen. Ron Wyden, an Oregon Democrat, teamed up with Ryan to redraft the Medicare proposal earlier this year.
Experts can argue about whether health care lends itself to competition or not. But doing nothing isn't an option. If the articulate Ryan can drive that point home, he will have advanced the debate.
Ryan's budget may not suit everyone, but it's a starting point. It calls for lowering tax rates - creating two flat income-tax brackets of 10 and 25 percent, and reducing the corporate rate from 35 percent to 25 percent - and eliminating loopholes. Almost everyone talks about lowering the rates and broadening the base; almost no one gets specific about the details.
Each year, the government loses an estimated $1 trillion to tax exemptions and deductions - known as tax expenditures, because they are really spending in disguise. The biggest losses are a result of the mortgage-interest deduction and the exclusion of employer-provided health-care benefits.
Taking on homeowners, many of whom are underwater on their mortgages, may be a stretch in an election year. But it will serve as an indication of just how serious a Romney-Ryan administration is about getting the debt and deficits under control. So far, neither has spelled out which loopholes he would close, which would probably be political suicide.
Ryan says his plan would eventually boost revenues as a share of gross domestic product to between 18 percent and 19 percent, which is close to the historical average, and reduce federal spending to 20 percent of GDP through cuts to non-defense discretionary outlays.
Ryan, as commentators have noted, is a direct descendant of Ronald Reagan, Jack Kemp, and supply-side economics. That means that, once the excitement about the GOP ticket dies down, Obama will have another catchphrase to deploy in his class warfare: "trickle-down economics."
Caroline Baum is a Bloomberg View columnist and the author of "Just What I Said."