Steve Greenhouse of The New York Times has a must-see story this morning on the political clout of the Service Employees International Union and its officials. The bottom line: SEIU is big, and SEIU knows it.

First key point from Greenhouse is that when SEIU president Andy Stern says jump, Democratic presidential hopefuls ask “how high?”:

After the union said it would not consider endorsing anyone who did not put forward a plan for universal health coverage, all the leading Democratic candidates produced one. When it demanded that the candidates spend a day in the shoes of a worker, Mr. Edwards, Mr. Obama and Mrs. Clinton did so, all spending a day with a health care worker.

The key to this power, of course, is the money. You can almost hear it: First we get the money, then we get the power, then we get the  White House:

The union has supported Republicans from time to time, sometimes infuriating the Democratic Party in the process. But for the most part, it backs Democrats. The union is expected to collect $40 million for its political action committee, which was the largest in the 2006 campaign. It plans to spend $30 million more in internal funds for getting out the vote and shining a spotlight on lawmakers who have helped thwart its agenda on national issues like expanding the State Child Health Insurance Program.

It’s worth reading the whole thing.