If Donald Trump reaches March 15 with a substantial lead in the polls, it will be difficult for any other Republican candidate to catch him.
Is Donald Trump nearing a tipping point after which it will be difficult for any other Republican to pass him in the presidential nomination race?
01:08 Trump attacks lead Democrat in Georgia congressional race21
14:50 Trump warns Democrats Obamacare will die without cash infusion13
14:49 U.S. scientists to protest Trump policies at Earth Day rally in Washington13
05:33 Paul, Jordan lead the Clippers back to a 111-106 victory over the Jazz, 2-1 series lead14