Last week, Harold M. Ickes seemed like Hillary Clinton’s only angel. This week, it is becoming clear that he is her undoing.

Exactly how Senator Clinton’s strategist has played such an important role in her presidential campaign becomes more obvious when you scrutinize not one Harold but two: Harold M. Ickes and Harold L. Ickes, his late father.

Harold M. has led Mrs. Clinton’s campaign using a traditional Democratic approach to politics, in which a party functionary works like crazy for a campaign that dispenses rewards to interest groups on behalf of the candidate. That approach worked phenomenally for Harold L. in 1936, when he was serving the New Deal as Franklin D. Roosevelt’s adviser and secretary of the Interior. But it turns out it’s ill-suited for victory today.

How Harold M., 68, came to make this error starts with his relationship to his father. Harold L. died when Harold M. was young. And the physical similarities between the two men aren’t especially great — Harold L. had that wonderful old-fashioned “office pudgy” look you don’t see a lot today.

When it comes to personality, the resemblance is almost eerie. Harold M. is enviably industrious. So was Harold L., who first won Roosevelt’s attention in 1932 by persuading the super delegates of his day, the progressives, that they ought to abandon the Republican Party.

Harold M. spews four-letter words when agitated. Harold L. was also pugnacious. Harold M. forced fellow strategist Mark Penn out of the Clinton campaign. Harold L. forced fellow New Dealer Harry Hopkins, not out, but down in the New Deal hierarchy.

“Sharp elbows must be genetic,” says journalist Jonathan Alter, who wrote “The Defining Moment,” a new book on FDR’s administration.

What about politics? As steered by Harold M., Clinton, 60, opened her campaign by reaffirming the traditional commitments to interest groups — unions, senior citizens, blacks. The man knows more about electoral politics than anyone except perhaps Karl Rove and Michael Barone.

How many other figures in public life can get granular on the 1964 election, as Harold M. did recently talking about Barry Goldwater’s loss to Lyndon Johnson in North Carolina? How many could have created Catilist, Ickes’s innovative for-profit database of voters and donors?

Some argue that it was here where the father actually differed. Mr. Alter says the elder Ickes’s emphasis wasn’t campaigning but government service and “on getting things done in a big bureaucracy.”

This is true, but Harold L.’s signature agency, the Public Works Administration, was a campaign vehicle so craftily designed it could have been thought up by the minds at Catilist. Today’s earmarks are ad hoc — lawmakers append them to laws when they can get away with it.

The PWA, by contrast, dispensed pork systematically. First, it queried towns on what buildings they might need — and then delivered checks for the desired school, swimming pool, or town hall. Harold M. innovates with databases. Harold L. innovated with power stations and civic auditoriums.

By today’s standards, the scale of the spending at Ickes’s PWA was stupendous — the equivalent of the federal budget for a year, then $6 billion or so. Every county but a few dozen got a PWA project.

Those in government immersed themselves in the campaign to reelect Roosevelt. At the 1936 Democratic Convention, one in 10 delegates was a federal employee. As obvious as it was — uncertain about black support, Roosevelt announced some new structures at Howard University just days before the presidential election — the strategy worked. It set off the great landslide victory of 46 out of 48 states.

The scale of that success stunned even Ickes: “I was not prepared for the surprising results that came over the radio Tuesday night,” he wrote in his diary. FDR won in spite of the strong dislike of a significant portion of the press. Added Ickes: “The outstanding thing about the campaign was the lack of influence of the newspapers.” No change on that today, either.

But the real takeaway from Ickes and 1936 is that buildings and swimming pools mattered enough to sway voters — apparently more than unemployment, which stood well over 10%.

In 1939, Congress found its balance and passed the Hatch Act to prohibit government employees from campaigning on the job. But that couldn’t stop urban renewal and Great Society programs for cities from giving an Ickesian victory to Johnson in 1964. And it didn’t preclude today’s Democratic Party from thinking in terms of blocs.

Until this week, Harold M. was still wagering that life might go on that way — and that he could win by nailing down delegates from interest groups in the way his father nailed down counties. But he and Mrs. Clinton looked backward once too often. The old political blocs just aren’t there the way they used to be.

Organized labor is dramatically smaller. Though Andy Stern of the Service Employees International Union wishes otherwise, workers in Mexico or Asia don’t vote here, and can’t help the Democrats. As Senator Obama has demonstrated, it’s possible to tempt blacks away from the party establishment’s candidate, even though that establishment had defined itself as serving blacks for three-quarters of a century.

Some voters think that by calling for “transformation” Mr. Obama is seeking an end to the loyal party of Ickes. You get the feeling Mr. Obama would view loyalty as toadying. What seems likely in any case, is that the next presidency will find its way without the House of Harold.

Miss Shlaes, a senior fellow of economic history at the Council on Foreign Relations, is a columnist for Bloomberg News.