Campaign 2016 updates: Donald Trump ally tweets caustic comment about Hillary Clinton

Lest there be any doubt that Donald Trump wants to nix Obamacare, he vowed on Tuesday to press for a congressional special session to repeal and replace the law.

But just exactly how Trump would follow through on the rare legislative procedure remained hazy.

During a speech in the Philadelphia suburbs dedicated to blasting the Affordable Care Act, Trump vowed, "When we win on Nov. 8 and elect a Republican Congress, we will be able to immediately repeal and replace Obamacare."

"I will ask Congress to convene a special session so we can repeal and replace, and it will be such an honor for me, for you and for everybody in this country, because Obamacare has to be replaced," he continued. "We will do it and we will do it very very quickly."

The Constitution gives the president the authority "on extraordinary occasions, to convene both houses [of Congress] or either of them."

But should Trump win, Congress would already be in session by the time he took the oath of office; lawmakers return to work on Jan. 3, while the presidential inauguration is Jan. 20. Those dates were enshrined into the Constitution with the 20th Amendment. 

Since the amendment was adopted in 1933, presidents have only exercised their power to convene Congress four times. Franklin Delano Roosevelt called two special sessions — one in 1937 in a failed attempt to pass new labor regulations and another in 1939 to adopt neutrality legislation in response to the start of World War II in Europe.

His successor, Harry Truman, twice convened Congress, in 1947 and 1948, in attempts to pass domestic legislation. No president has exercised that power since.

It appears Trump is still working out the logistics of his plan. During a post-speech trip to Wawa, the gas station and food vendor with a cult following, Trump was asked whether he had spoken to congressional leaders about his desire for a special session.

Not yet, Trump replied, adding, "We will very soon."