WASHINGTON (Reuters) - U.S. Democrats and Republicans on Tuesday showed no sign of resolving an impasse over taxes that has stalled budget negotiations and could threaten the country's top-notch credit rating. (http://feeds.feedburner.com/~ff/reuters/topNews?d=yIl2AUoC8zA) (http://feeds.feedburner.com/~ff/reuters/topNews?i=QW3xWlq-CMY:X3CeF4exrq0:V_sGLiPBpWU) (http://feeds.feedburner.com/~ff/reuters/topNews?i=QW3xWlq-CMY:X3CeF4exrq0:-BTjWOF_DHI) (http://feeds.feedburner.com/~r/reuters/topNews/~4/QW3xWlq-CMY)