If you haven't seen it yet, there's plenty of video of VP Dick Cheney getting the Bronx cheer (Anacostia cheer?) when throwing out the first ball at the Washington Nationals' home game. The booing has gotten the expected spin—Cheney's the most unpopular guy in the administration, all their poll numbers are down, etc.
But maybe that's too simple. Maybe it's just pointless to have the president (or his bumbling sidekick) throw out the ball at DC games if said president is a Republican. When he's in DC, a Republican president is in the heart of the part of America that most hates his guts. In 2004, DC gave George W. Bush only 9% of its votes—around 21,000. Almost 10 times as many Washingtonians voted for John Kerry, his "issues" with ball-throwing having been clearly established. And even though the Nationals depend on the Maryland and DC burbs to fill out the stands, that hardly fixes it. Virginia's Arlington County went for Kerry over Bush by 36 points. Maryland's Montgomery County and Prince George's County went for Kerry by 33 and 64 points, respectively.
Basically, unless the Republican party starts winning vast numbers of liberal or black votes, they're not going to be able to send the presidents into DC ballparks without getting booed. Maybe this is what Dick Morris was going on about.