Senate Majority Leader Harry Reid, D-Nev., seemed truly ready go "nuclear" before last-minute concessions from Republicans averted a showdown over the 60-vote filibuster rule.

Reid had been issued frequent nuclear warnings, so why did he decide to finally draw a line in the sand -- as opposed to, say, back during the debt limit showdown of 2012?

The answer is that the votes he was planning were mainly for nominees to federal agencies that Big Labor has been aggressively pressuring Democrats to fill.

These include: Labor Secretary nominee Thomas Perez; Consumer Financial Protection Bureau Director Richard Cordray; and five National Labor Relations Board nominees.

All of them except Cordray deal directly with labor issues -- and labor likes him too. Once installed, these Obama appointees would give the Labor Department, the NLRB and the CFPB strong liberal voices.Cordray's nomination was advanced after Obama agreed to drop two contested recess appointments to the NLRB and put two new picks to a confirmation vote.

Communications Workers of America President Larry Cohen was miffed that Reid hadn't acted earlier.

"Democratic leadership: You need to act. These rules have not worked the entire time this president has been in office. What are you waiting for?" he said the previous week.

The NLRB, which oversees business-labor relations, was the unions' main concern, because it has recently considered numerous rules changes pushed by labor, including speeding up workplace representation elections, limiting the rights of rank-and-file members to demand audits of union spending and telling businesses they must post notices explaining how to unionize.

An appeals court hobbled the NLRB in January by ruling that Obama's unilateral recess appointments of Richard Griffin and Sharon Block were unconstitutional. That left the board without a quorum and invalidated much of its recent work. Other court rulings have also dealt serious setbacks to the pro-labor board.

The NLRB can still act -- it has career staff that does most of the day-to-day work -- but, without a quorum, unions cannot appeal to the board to resolve disputes or enforce actions.

The Supreme Court is set to hear the recess appointee case later this year, but labor leaders doubt the justices will rule in their favor.

Even if the recess appointments were upheld, current NLRB Chairman Mark Pearce's term runs out next month. That would again leave the board without a valid quorum unless the Senate approves Obama's nominees.

Hence the pressure from labor on the Democrats. Cohen warned last month that Reid would get "lots" of the blame if the filibuster didn't end soon.

So it wasn't too surprising that Reid decided to issue his ultimatum - and that his list of GOP filibuster abuses concluded with the NLRB nominations.

"The results of contested union elections could be thrown out. And labor abuses and unfair employment practices would go unchallenged," Reid warned.

And this, he argued, was reason enough to end the minority's check on the Senate's power.

Republicans earlier relented on Perez and Cordray but refused to vote on Griffin and Block's NLRB renominations, arguing that the recess appointments have tainted them. The other three were fine, they said.

That wasn't a concession from the Democrats' perspective. Two of those NLRB nominees are -- by Senate tradition -- Republican picks. So just voting on Pearce and those two would have given the board a 2-1 GOP majority.

The deal ultimately had the Democrats dropping Block and Griffin and the GOP promising votes on whomever the White House picks to replace them.

This means there will soon be a 3-2 Democratic majority on the NLRB -- exactly what Big Labor wanted all along.