“We built it,” the slogan of the evening, was painted on the side of the convention hall. Speaker after speaker alluded to the phrase in an entire day based on the thinnest of reeds — a poorly phrased remark by the president, deliberately taken out of context. President Obama was making the obvious point that all businesses rely to some extent on the work and services of government. But Mr. Romney has twisted it to suggest that Mr. Obama believes all businesses are creatures of the government, and so the convention had to parrot the line.

“We need a president who will say to a small businesswoman: Congratulations, we applaud your success, you did make that happen, you did build that,” said Gov. Bob McDonnell of Virginia. “Big government didn’t build America; you built America!”

That was far from the only piece of nonsense on the menu, only the most frequently repeated one. Conventions are always full of cheap applause lines and over-the-top attacks, but it was startling to hear how many speakers in Tampa considered it acceptable to make points that have no basis in reality.