Donald Trump promised Tuesday that if he is elected president, he would immediately call Congress into special session to repeal Obamacare.

In a speech heaping criticism upon President Obama's healthcare law, the Republican presidential nominee vowed that he would work to ditch the measure as one of his first actions as president.

"I will ask Congress to convene a special session so we can repeal and replace it," Trump told a crowd in King of Prussia, Pa. "And it will be such an honor for me, for you and for everyone in this country.

"We will do it and we will do it quickly," Trump added. "It is a catastrophe."

Enrollment in the Affordable Care Act's marketplaces began Tuesday for the fourth year. Trump and Republicans have been hitting hard against the healthcare law in the past week, since the Obama administration released the 2017 marketplace offerings, which show higher prices and fewer choices for consumers.