He also renewed threats to cut forces in Germany, attacking Chancellor Friedrich Merz after criticism of Washington's Iran war strategy.
Asked at an Oval Office event about bases in Spain and Italy, Trump said "probably", calling Italy unhelpful and Spain "horrible" over their refusal to join the conflict.
German officials played down the threat as a repeat of Trump's first-term stance, while Merz later stressed NATO and US ties and criticised Iran for shunning peace talks.
Are threats to pull troops from Europe a negotiation tactic or the start of a major US strategic pivot from the continent?
How has the US-Iran conflict unintentionally given European allies more leverage to assert their own foreign policy independence from Washington?
With the Strait of Hormuz blockaded, can a new international coalition succeed where unilateral US pressure on Iran has failed?