Washington (CNN) At 5:00 a.m. Friday, with the moon still beaming over Washington, the Capitol buzzed with activity.

The subway trains that connect the Senate office buildings to the Capitol hummed. Elevator operators stood by the "Senators Only" elevators, waiting for riders.

Bleary-eyed senators arrived at the Capitol for an unusual session that ultimately became the longest vote in modern history. It was all so the four Democrats who were on the presidential debate stage in Miami Thursday night -- Sens. Bernie Sanders of Vermont, Michael Bennet of Colorado, Kamala Harris of California and Kirsten Gillibrand of New York -- could return to Washington to vote. But also, so the remaining senators -- anxious to get home for the Fourth of July recess -- could leave as soon as possible.

Acceding to Democratic demands to hold the vote Friday, GOP leaders twisted and turned normal procedures and practices to make the session work. That meant convening before sunrise (on a day they were supposed to be gone), allowing Democrats to preside over the chamber (rather than Republicans), keeping the vote open for a record-breaking length of time (rather than the usual half hour or so), and agreeing that, if the amendment were to pass, it would retroactively be added to a defense authorization bill that had passed the Senate the day before (which is practically unheard of).

Everyone also knew the amendment, which would require President Donald Trump to get congressional approval before launching military strikes against Iran, was not going to get the 60 votes it would need to advance. But the measure is a top priority and serious issue for Democrats who pressed GOP leaders to schedule the vote regardless of the outcome.

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