President Obama got booed on Monday after making a joke about a trade. He should have known better.

Some things just aren't OK to joke about.

Red Sox Nation sent that message to President Obama Monday at a fundraiser in Boston. The president, a staunch fan of his hometown White Sox, was goofing on a trade this week that sent third baseman Kevin Youkilis to the south-side Chicago squad. "Boston, I just want to say thank you for Youkilis," Obama said. Met with boos, he went on: "I'm just saying he's going to have to change the color of his sox. I didn't think I'd get any boos out of here. I guess I should not have brought up baseball. I understand, my mistake, my mistake. You gotta know your crowd."

Truer words, Mr. President, have never been spoken. In today's political sphere, where even Social Security -- long said to be the nation's third-rail -- has been targeted for reform by both parties, the Red Sox may be the only thing that can reliably guarantee backlash for a candidate. The rule holds true even for Democratic superstars in deep-blue Massachusetts.

The Romney campaign, based in Boston, was quick to respond with umbrage: "The Red Sox have suffered many setbacks over the years -- the Babe Ruth trade, the ball through Buckner's legs, the Bucky Dent home run. Maybe the President should have congratulated the team for winning the World Series in 2004 and 2007. Instead, he chose to mock them for trading away one of its favorite players at a time when the team is struggling." (As some wags pointed out, Romney has been much slower to articulate a position on immigration than on the trade.)

What the incident shows is that Obama hasn't studied his history closely enough. Bryan Curtis persuasively showed how Obama -- like Richard Nixon -- wields his sports fanaticism as a tool to assert his legitimacy and associate with the American Everyman. But he should know better than to mess with the Red Sox. Here's what has happened to politicians who haven't heeded that advice in the past:

  • Famously, Massachusetts Attorney General Martha Coakley lost a 2010 race to now-Senator Scott Brown after a bumbling campaign that included two baseball-related missteps. First, she asked with mock horror if she was supposed to stand "outside Fenway Park? In the cold? Shaking hands?" Worse, when she was told that Red Sox hero Curt Schilling had endorsed Brown, she apparently had no idea who the pitcher (a righty in baseball and politics) was, and dismissed him as "another Yankee fan." To get a sense of how visceral the reaction was, one blogger referred to the comment as "slander."
  • Brown hasn't been immune. In this year's race against Elizabeth Warren, Democrats have gleefully pointed out that the Republican senator has accepted the maximum allowed donation from the president of the hated Yankees -- or as a columnist in the conservative Boston Herald put it, "the evil empire."
  • Warren, for her part, could use a refresher in baseball trivia. Asked to name the last two Red Sox World Series titles, the Oklahoma transplant guessed 2004 and 2008. She was half right: The correct answers are 2004 and 2007.
  • Perhaps unsurprisingly, Senator John Kerry has also been mocked for failing to relate to the home team. He managed to claim that his favorite Red Sox player of all time was Eddie Yost (the third baseman played for nearly 20 years, but his career was spent in Washington, Detroit, and L.A. -- though he did do a stint as a Red Sox coach after retiring) and also referred to the star "Manny Ortez," a hamhanded portmanteau of Manny Ramirez and David Ortiz.

But Romney should be careful, as he isn't on totally solid ground himself. The former Massachusetts governor in 2007 failed to identify Fenway anthem "Dirty Water," much to Boston sports fans' horror.