Last summer, not long after Donald J. Trump secured the Republican nomination for president, his recently installed campaign manager, Stephen K. Bannon, met with top officials from the Republican National Committee to discuss management of the general election.

Mr. Trump’s staff had remained unusually small throughout the grueling primaries — a compactness, his advisers believed, that had given them a nimble edge. Now most Republican officials expected the Trump team to expand as it began to oversee the thousands of Republican staff members, state officials and consultants who would be ground troops in the coming political war.

But when Mr. Bannon met with R.N.C. officials, he informed them that a major expansion was not going to happen.

The Trump campaign, he said, intended to remain sparse and decentralized. Borrowing a Silicon Valley mantra from Facebook, he told his shocked listeners that “your job is to move fast and break things,” according to a person who was present. “Figure out what needs doing, and then just do it. Don’t wait for permission.”