The nuclear codes.

They're a topic of conversation that have repeatedly surfaced in 2016, largely due to Donald Trump's unpredictable temperament and repeated suggestions that he could envision scenarios in which he would possibly use a nuclear weapon.

“I’m not going to take any cards off the table,” the Republican presidential nominee said earlier this year. “[T]he thought of it is horrible, but I don’t want to take anything off the table.”

Hillary Clinton, Trump's Democratic opponent, has capitalized on such rhetoric, often warning that the New York billionaire can't be trusted with the nuclear codes.

But could a president make the decision to use a nuclear weapon without any interference from others?

Bruce G. Blair, a former Minuteman missile-launch officer and research scholar at Princeton University’s Program on Science and Global Security, told Business Insider that the answer, essentially, is yes.

Blair pointed to a step-by-step outline of the nuclear chain of command which he helped describe in Bloomberg earlier this month.

Here's what would happen, according to Blair: The president would consult with top military brass about the use of a nuclear weapon. The president would come to a decision. The order would be verified and officially issued. The launch crews would take over. And, finally, the missiles would be deployed.

If the threat wasn't imminent, he said it would likely take a few days to prepare the weapons. But, if in the middle of a sustained conflict during which nuclear weapons had been on the table as a last resort, the process would be vastly accelerated — missiles could be in the air within a window as small as 15 minutes.

Congress could do nothing to stop the decision if it were made in haste, Blair said.

"I mean, the Constitution of the United States designates the president as commander in chief, and there is no wiggle room there," he said. "And of course, Congress passed the War Powers Resolution in 1973 that allows for the president to deploy armed forces for up to 60 days without congressional approval. By law, by custom, Congress has bowed out of the process."

Blair did add that there is "a protocol and requirement" for NATO consultation, and if there was not consent by the country responsible for launching the weapon, "it's sort of open to question" whether they could "effectively veto" its use.

For example, if the weapon was to be delivered from the nuclear base in Germany, where the US shares weapons, and dropped by a German plane, Germany could potentially ignore the order.

"You're getting into kind of fuzzy territory there," he said.

The only measure that could be taken at home, Blair said, is the invoking of Section 4 of the 25th Amendment of the Constitution — which has never been used.

That section allows for the vice president, together with a majority of cabinet heads or Congress, to declare the President disabled and unfit to execute the duties of the office. The vice president, which in this case would be either Trump's running mate, Mike Pence, or Clinton's running mate, Tim Kaine, would have to submit a written declaration to the Speaker of the House and President pro tempore of the Senate explaining why the president was unable to fulfill his duties. If approved, the vice president would then take over.

Blair called that "the only thing" government officials "could possibly do" in such a situation.