How can this be? Unions give more than all industry combined to political candidates.

Over the past 20 years Unions own the political giving league tables.  Note that the teacher's unions are called out separately and have donated close to three times as much to politicians as the entire Energy industry.  Almost all to Dems, natch.  The natural argument to make is 'well, when you add up all of the corps their totals probably almost equal the union totals' - except that all of the corps are representing far more human beings (their employees and investors), while the Unions represent only 1 in 8 US workers.  On a per constituent basis union political giving has to be 10 or 20 times corporate giving.  And corporate giving includes the lawyers!

Money power is alive and well in American politics.  It's just that it's disproportionately union power.