Article cites Bloomberg politics polls, not the rate of campaign cash donations.
Los Angeles Timmes
Union leaders seem to be ignoring their members cries for supporting Bernie Sanders
In These Times
Examples of grass-roots union support for Bernie Sanders
A Union President chose Hillary over Bernie because "we need to win."
Campaign Donation Limits Are Irrelevant, Just Look At Bernie Sanders And Ben Carson's Small Donor Cash-In
Small donors are far from reaching their contribution limits, and they can donate again.
Look how much cash Bernie Sanders has raised so far.
Other media outlets are glomming onto the the counter-intuitive union endorsement of Hillary Clinton, who hasn't really been fighting for labor as much as Bernie Sanders.
One union leader said he personally loved Bernie but endorsed Hillary because he thought she had a better chance of winning, but the media and the union leadership cannot see the groundswell of support for Bernie coming from the rank-and-file.
It appears the media are presupposing a Clinton advantage based on the assumption that union leaders held a vote among the members. I couldn't find the rules for endorsing candidates, but The Daily Caller reported that Bernie and Hillary met with union leaders in a private meeting. which suggests that the rank-and-file union members don't have much of a voice in the matter.