When someone accuses you of being “un-American” you reach across the table and smack him upside the head, or you unleash a verbal attack on him that he won’t soon forget. U.S. Sen. Sherrod Brown, a veteran of Ohio Democratic Party bare-knuckle politics, did neither when his challenger, Republican state Treasurer Josh Mandel, described him as “un-American.”

Brown and Mandel had appeared together at a meeting with Columbus Dispatch editors and reporters when the first-term treasurer tossed out the ridiculous charge against the senator.

Here’s what Mandel said, according to the Dispatch:

“I don’t toss around the word un-American very often — it’s a dangerous word to use. But stripping … Delphi employees of their pensions with that vote — that is un-American.”

How did Brown respond? By launching into a history of the collapsing American auto industry in 2009 and 2010 and defending his vote for a federal bailout of General Motors and Chrysler.

The Dispatch reported that the senator did not say anything about the “un-American” label. One of his campaign aides later told the newspaper it was disrespectful.

That’s the best Democrats can do when their patriotism is questioned? Have they forgotten how Mandel conducted his campaign for state treasurer in 2010 against incumbent Kevin Boyce, a black Democrat?

It’a one thing for Barack Obama to respond presidentially when Republicans accuse him of being a socialist, charge that his birth certificate is a fake, and that he is determined to sell America down the river.

It’s quite another for a U.S. senator to allow a challenger to denigrate him without hitting back.