The former President also warned that Russia’s Vladimir Putin “is zero-sum. He can’t think, ‘How can we both win?’ He only thinks, ‘How do I win, you lose?’”
Russia has denied trying to influence the November 2016 vote but US intelligence agencies concluded it had.
Mr Trump has previously downplayed the findings but last year said he was “with our agencies, especially as currently constituted with the leadership”.
Mr Bush said it wasn't clear if Russia's "meddling" directly affected the election, though he said it was clear they tried. "It's problematic that a foreign nation is involved in our election," he added at a conference in Abu Dhabi.
Former FBI director Robert Mueller is currently investigating alleged links between the Kremlin and Mr Trump’s campaign team.
Several people including the Republican’s former national security adviser, Michael Flynn, have been charged.
Mr Trump denies any such links, and has called the investigation a “witch hunt”.
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