Wall Street trembled when Republicans first began threatening to force the United States into default by not raising the federal debt limit, but after four years of fiscal standoffs, the threat looks increasingly like a bluff and the markets are calling it. A Reuters analysis, tracking short-term Treasury yields, credit default swaps and market volatility data, showed traders are increasingly less likely to respond to repeated ultimatums from Republicans in the U.S. Congress about the debt limit. For now, after five years of fighting, the debt limit battles on Capitol Hill have gone quiet.