A government shutdown would be painful enough in good economic times, but with the U.S. economy struggling at a bare 2.5% annual growth rate, even the modestly depressed spending from a government shutdown would be harmful and perhaps disastrous. If a shutdown runs for three or four weeks it could cause significant economic damage, reducing the U.S. Gross Domestic Product by 1.4 percentage points for the quarter, according to Moody’s Analytics economist Mark Zandi.