What's stopping the US from striking Iran despite Trump's threat?

After days of publicly threatening Iran, US seems to be holding off on immediate military action. White House is busy consulting allies about timing for the operation and whether it would "meaningfully" destabilise Ayatollah Khamenei's regime, Axios reported. Officials are weighing the risk of retaliation as US wants to 'punish' Iran without triggering a broader regional war in West Asia.