With the prospect of reduced Colorado River deliveries as early as 2018, U.S. and Mexican negotiators have been in a race against the clock to forge an agreement that involves sharing any future shortages — and are hoping for a signing before President-elect Donald Trump takes office on Jan. 20. Water managers on both sides of the border say the accord will be crucial in spelling out how the U.S. and Mexico would take cuts when a shortage is declared on the river, a lifeline for some 40 million people in both countries.