US President Donald Trump, in a telephone interview with TIME magazine, did not rule out the possibility of sending ground forces in the war against Iran, TIME reports.

Trump said he believes the objectives of the campaign could be achieved within four or five weeks, though he concedes the timeline could stretch longer. The war will continue, he suggests, until those objectives are accomplished. “I have no time limits on anything,” he said. “I want to get it done.”

Trump described the mission as preventative. “America First is really about keeping America healthy and well, and not having other countries, you know, hit us,” he said. “There are occasions when you have no choice. This was an occasion.”

The aim, he said, is to prevent Iran from having the capacity to endanger the US. “They can’t have a nuclear weapon. That’s number one, two, and three. Number four, no ballistic missiles,” he said.

Another objective, Trump said, is installing “somebody that is rational and sane” to lead Iran.