Say what you want about Bill Clinton, he gives a great speech, and last night's was no exception. There's already buzz about a "Bubba bounce," and if President Obama tonight manages to top the speeches delivered by Bill and Michelle, there's little doubt the conventions will end up giving his reelection chances a boost.

But of particular note in last night's speech was the clarity with which Clinton deconstructed the Republicans' economic claims—their critique of Obama's job performance and their promise to take the country in a new and more prosperous direction. "The Romney plan fails the first test of fiscal responsibility," explained Clinton to a rapt audience. "The numbers do not add up.”

The same, of course, could be said of Rob McKenna.

#Arithmetic has been trending on Twitter since Clinton's speech, and that's bad news for conservative Republicans like McKenna who have liberally sprinkled their rhetoric with shoddy math. If the Democrats manage to sustain this meme throughout the fall campaign, it won't just prove toxic to Romney, but to all Republicans who have pinned their election hopes on the gamble that voters and journalists wouldn't eventually whip out their calculators.

Romney was never going to win Washington, but this is not just about political coattails. For if the presidential campaign educates swing voters to understand that the entire Republican agenda is a mathematical fraud, the promises of down-ticket GOP candidates will be eyed just as skeptically.

Clinton's speech last night was more than just a great convention speech. It was more than just a devastating refutation of Mitt Romney. Clinton's speech is a roadmap for countering the entire Republican economic agenda in six simple words: "The numbers do not add up." And simply forcing Republicans to attempt to make the effort to show that they do, changes the tone and tenor of the debate.