Gil Troy, a professor of history at McGill University, is the editor, with Arthur Schlesinger Jr. and Fred Israel, of “History of American Presidential Elections, 1789-2008,” fourth edition.

In running for re-election, Barack Obama commands the most powerful democratic platform in world history and the greatest backdrop, the White House. A seemingly casual announcement in a TV interview can trigger a political earthquake, as Obama did when he endorsed gay marriage. But the president’s magnificent residence can also be what Harry Truman called the Great White Jail. 

Presidents are handcuffed by their power. Presidential statements can crash financial markets or start wars. The dignity of the presidency also inhibits, even in today’s brutal political environment. Obama’s campaign ad attacking Mitt Romney’s record at Bain Capital made some Democrats squirm as Republicans labeled the president “another gut-punching politician from Washington.”

The ambivalence about presidents politicking goes back to the nation’s founding. George Washington liked “going on tour,” getting “huzzahed” north and south – but, reflecting his contemporaries’ distaste for democracy, he avoided explicit political talk. When the less popular President Martin Van Buren toured before his 1840 re-election campaign, his fellow Democrats feted him. Nevertheless, the new partisanship polarizing American politics had Whig Party critics denouncing Van Buren’s activities as “undignified” and “insulting,” while mocking “His Majesty, King Martin the First.”...