One of the longest votes in the recent history of the Senate is underway now.

A fight on the Senate floor - and an ill senator, flying in from North Dakota - has delayed a vote on the nomination of Todd Jones to lead the Bureau of Alcohol, Tobacco, Firearms and Explosives.

A 15-minute routine vote is now expected to take more than four hours.

Arm-twisting, cajoling and persuasion came into rare public view on the Senate floor, with an agreement to avoid filibustering President Obama's nominees coming perilously close to breaking down.

Sen. Lisa Murkowski, R-Ala., initially voted against moving ahead with Jones' confirmation. Her decision meant the Senate was one vote short of 60 votes needed, so a timeout was abruptly called as a cluster of senators surrounded Murkowski on the Senate floor.

Democrats urged Murkowski to switch her vote. Republicans implored her not to.

As the conversation intensified, Sen. Susan Collins, R-Maine, swooped in to rescue Murkowski. The two left the Senate floor for a private conversation.

"I was concerned she was being pummeled and might need a break," Collins later told ABC News.

Finally, Murkowski returned and changed her vote in favor of proceeding to a final passage on the Jones confirmation.

But the vote won't be official until tonight, when Sen. Heidi Heitkamp, D-N.D., flies back to Washington. A spokeswoman said she became ill in North Dakota and was delayed returning to the Capitol this week, but was scheduled to arrive around 6:30 p.m.

It was the latest bit of drama surrounding the ATF, an agency that has been without a permanent director since 2006 when the Senate was given the power to confirm the director.

Jones, who was nominated by President Obama in January following the deadly massacre at Sandy Hook Elementary School, has served as the acting ATF director since 2011, while continuing his work as a U.S. attorney in Minnesota.

The Senate Judiciary Committee voted to send Jones's nomination to the full Senate strictly along party lines with a vote of 10-8 earlier this month. Republicans used the nomination of Jones to raise deeper questions about the ATF.

It was an unusual bit of Congressional theater that offered a window into the new spirit of cooperation that was reached earlier this month after Senate leaders threatened to invoke the so-called nuclear option to change filibuster rules.

The Senate leaves this week for an end-of-summer break, so Senate Majority Leader Harry Reid is eager to get this vote finished. He has the authority to extend the vote as long as necessary.

"If there was ever a test of whether the Senate could move forward in a bipartisan way, this afternoon was it," said Sen. Amy Klobuchar, a Minnesota Democrat who helped lead the Jones confirmation fight. "The last thing we want right now is to leave with a radioactive blowup."

The vote over Jones is expected to be held open for more than four hours. It is a vote for cloture - or to end debate - to be followed by the final confirmation of Jones, which requires only 51 votes.

The last time such an extended vote took place was 2009, the Senate Historian's Office believes, on the $787 billion stimulus package.

The vote was held open on Feb. 13, 2009, for five hours, from 5:30 p.m. to 10:30 p.m., for Sen. Sherrod Brown, D-Ohio, who had been at a family funeral. With the outcome of the vote on the line, the White House sent a plane for Brown.