Despite all the hot fiscal cliff rhetoric, the differences between President Barack Obama and House Speaker John Boehner seem relatively narrow. So why haven’t they shaken hands already? One answer: Both sides need to keep — or get — their own troops behind them. …

Chastened by Obama’s re-election, Boehner has violated a quarter-century of Republican dogma by offering to raise taxes, including boosting income tax rates on earnings exceeding $1 million annually. Eager for a budget deal that would let him move on to other issues, Obama in turn would cut the growth of Social Security benefits, usually off-limits to Democrats. He also would impose tax increases on a broader swath of people than millionaires — those with incomes over $400,000. But that figure, too, is a retreat from what he campaigned on: the $200,000 income ceiling on individuals and $250,000 on couples.

That means both men have angered lawmakers and staunch supporters of their respective parties, just when the need to retain that support is crucial. Neither wants to risk his political capital by embracing a deal his own party rejects.