A retired US general argues the Pentagon's top brass failed to warn Trump that airstrikes alone cannot topple Iran's regime — bad news for anyone expecting a quick military win.

• Iran's key facilities are built deep inside granite mountains, designed like America's own nuclear-proof bunkers, and no bomb in the US arsenal can destroy them.
• The US can hit anything on the surface and beat Iran's air defenses, but the country is as big as Western Europe and America lacks the ammunition to carpet bomb it.
• Toppling the regime by force would take a million-man army and massive casualties, and military leaders should have said so from the start instead of cheering the plan on.
• The strike that hit a girls' school points to sloppy targeting as the campaign dragged on, since early targets get vetted carefully but later rounds get far less research.

Outlook: Expect more targeting mistakes and no regime collapse as long as the campaign relies on airpower alone.