WASHINGTON — The debate on global warming and energy policy accelerated on Tuesday as two senior House Democrats unveiled a far-reaching bill to cap heat-trapping gases and move the country quickly from dependence on coal and oil. But the bill leaves crucial questions unanswered and as of now has no Republican support. For those reasons, it marks the beginning, not the end, of debate in the current Congress on how to deal with two of President Obama’s top priorities, climate change and energy. The draft measure, written by Representatives Henry A. Waxman of California and Edward J. Markey of Massachusetts,...