In the failed fight to stop fast track, organized labor spoke—largely—with one voice. The main U.S. union federation, the AFL-CIO, announced a temporary freeze on PAC contributions, and its affiliate unions mostly complied. Unions across the industry spectrum warned Democrats against siding with Obama on trade. Some big unions were quieter than others, but none defected to shield the president. “It was a unifying moment,” says Harold Schaitberger, president of the International Association of Fire Fighters.

The same can’t be said for labor’s presidential endorsement process. “Some want to wait, some want to move,” International Association of Machinists and Aerospace Workers President Tom Buffenbarger told Bloomberg last month. “Some are just so pissed off that they just don’t want to do anything.”

This week, Democratic 2016 hopefuls Bernie Sanders, Martin O’Malley, Lincoln Chafee, and Jim Webb will court organized labor at the Iowa AFL-CIO’s annual confab. Last week in Maryland, Sanders, O’Malley, and Webb—along with prohibitive frontrunner Hillary Clinton and Republican Mike Huckabee—each met privately with the union leaders who comprise the national federation’s executive council. Labor leaders “were encouraged by our discussions,” AFL-CIO President Richard Trumka said in a July 30 statement.

But divisions abound. A month ago, after the AFL-CIO’s South Carolina and Vermont chapters passed pro-Sanders resolutions, the AFL-CIO sent a memo reminding its state subsidiaries that (unlike the AFL-CIO’s affiliated unions) they aren’t allowed to make their own presidential endorsements. Leaders of affiliate unions who sit on the executive council tell Bloomberg that Trumka also urged them to hold off on making presidential picks until the council got to meet the candidates July 29 and 30. (The AFL-CIO declined to comment about private conversations.) “He’s trying to actually do what he did in trade, and that is to keep the unions together, to use their most effective voice collectively,” National Nurses United Executive Director RoseAnn DeMoro told Bloomberg last month. But given the autonomy of the individual unions, she said, “He’s got the power of persuasion—that’s the only thing he has.”

Not everyone wanted to wait. The 1.6 million-strong American Federation of Teachers endorsed Clinton July 11, raising hackles among some union leaders and raising expectations that more could soon follow. But on July 20, the federation’s political committee voted unanimously to recommend that the AFL-CIO itself keep waiting before endorsing anybody.

“On this issue, every union has their own process, and no union is going to delegate that process to the AFL-CIO,” says AFT President Randi Weingarten. In AFT’s meetings with Democratic contenders, she told Bloomberg last month, “They were all terrific, but Hillary really made an impression on people in terms of the way in which she answered the questions, not just the responsiveness, but really leaning in, being frank, being candid, resonating with people.” As for Clinton’s democratic socialist rival, she said, “Both in terms of Sanders and Trump, people are pissed with the way that life has treated them, that the economy has treated them, and I totally understand that passion. But there’s a difference between a message and actually having a plan to win.”

Amalgamated Transit Union President Larry Hanley says AFT’s endorsement puts heat on other unions. “Once the line breaks, there’s more pressure on others—they start saying, ‘Gee, I should’ve been the first,’” says Hanley, who like Weingarten backed Clinton’s failed 2008 presidential bid and her successful 2000 Senate race. (Hanley says his support that year included using his size to block cameras from capturing a controversial supporter giving Clinton a hug.) “That’s the strategy behind getting AFT to move, is that it’s going to start bringing pressure… If I were Hillary Clinton, I’d do the same thing.” Hanley attended a July 13th meeting with Sanders at the headquarters of the American Postal Workers Union; organizers say 47 leaders from 22 unions were present. The ATU head told Bloomberg he’d gladly back Clinton again if she’d start sounding more like Sanders and Elizabeth Warren. “When we go out and say, ‘look, we need a $15 minimum wage nationally,’ but then support a candidate who says, ‘I’m against that,’” he says, “we have a problem.”

Such divisions aren’t unusual. In fact, they’re built into the structure of the AFL-CIO: A federation of 56 unions; spanning public and private sector; service, manufacturing, and more; with little authority to mandate what those affiliates do, and an inclination towards inaction in the absence of consensus. In 2012, when Republicans insisted an FAA reauthorization include changes making it harder for airline and railroad workers to unionize, 19 unions urged Democrats and Obama to reject the deal (one called it “our Wisconsin”), but a few others endorsed it (“that compromise was necessary,” one said when it passed). The AFL-CIO itself stayed silent, the Democratic Senate passed the bill, and Obama signed it.

There are also deep disagreements among unions (within the AFL-CIO, and outside it) on issues ranging from energy policy, to military spending, to which issues unions should care about in in the first place. The AFL’s last quadrennial convention was defined by tensions between affiliates that believe organized labor needs to more aggressively embrace progressive causes like criminal justice reform and allies like environmentalists, and those that believe it should focus more narrowly on “worker issues,” and build better bridges with Republicans.

When it comes to presidential politics, the federation moves slowly by design. Its rules require two-thirds support before it can endorse a candidate. While individual unions sometimes gamble—two of the biggest ones endorsed Howard Dean in November 2003—the federation tends to play it safe, waiting until a Democratic nominee is clear. In recent decades, the AFL- CIO’s riskiest (still not very risky) endorsements were of frontrunner Al Gore in October 1999, and frontrunner Walter Mondale in October 1983.

While Clinton holds a commanding lead, there are sharp disagreements over what strategy will produce the most pro-labor president. Endorse Clinton early to get to work battling the GOP? Hold off to extract more concrete commitments? Take a chance on Sanders as a vehicle to build a mass movement? Gregory Junemann, president of the International Federation of Professional & Technical Engineers, warns against a premature endorsement. “It’s like tipping the cab driver before you get in the car—the person then has your commitment without making any promises themselves,” he says. In contrast, IAM head Buffenbarger says there’s little advantage in holding out for election season promises, because candidates don’t stick to them anyway. “When they find their way to the front door of the White House, they seem to forget about it as soon as they cross the threshold,” he says.

Disappointment with Obama’s record—from a labor law reform he didn’t prioritize, to a healthcare law unions want changed, to a trade pact they despise—unites the AFL-CIO’s most liberal and most conservative affiliates. But different leaders take different lessons from it: Does it mean they would’ve been better off fighting harder for Hillary in the 2008 primary, or that it’s time to stop trusting mainstream Democrats?

For a swathe of organized labor, Clinton’s equivocal stance in the summer’s high-profile trade battle complicates the calculation. So does Sanders’ traction with some unions’ activists and local staff. “Bernie knocked it out of the park; Hillary was just plain old politics,” Los Angeles union representative and 31-year union member Bill Shaver said after watching Sanders urge “political revolution” in a July 28 speech to his union, the International Association of Sheet Metal, Air, Rail and Transportation Workers. (A pre-taped video from Clinton preceded Sanders’ speech.)

Sanders received 65 percent support in a poll of delegates at the Utility Workers Union of America’s July convention. At IFPTE’s conference last week, says President Junemann, delegates delivered effusive speeches in favor of endorsing Sanders; the proposal was deferred to the union’s executive council, in part because some members are still holding out hope for Joe Biden. Clinton backers note she’s got grassroots support too: Weingarten cites over 3-to-1 support she received in a poll of AFT members who vote Democratic and wanted to endorse someone, and a rapturous reception at the AFT conference when the endorsement was announced.

While the AFL-CIO itself likely won’t choose a candidate for a while, labor leaders expect more unions will roll out their own endorsements—most, but not all, for Clinton—over the next few months. “The Koch brothers got boots on the ground right now,” says Lee Saunders, president of the American Federation of State, County & Municipal Employees and chair of the AFL-CIO executive council’s political committee. “We’ve got to put boots on the ground.”

In Iowa this week, Clinton’s rivals will get another chance to sway union officials, appearing (separately) on stage to field questions from Trumka and other labor leaders. Those on- stage Q&As, and the chance to mingle with union members, also offer the chance to build their base of rank-and-file supporters, which those backing the long-shot candidates say matters more than endorsements. “This era of endorsements in 2015, at best it’s hollow; at worst it’s an effort to control people, which people hate,” says newly-retired Communications Workers of America President Larry Cohen, Sanders’ highest- profile union surrogate and volunteer. “The much more important thing for us is unleashing the members.”