(JNS) U.S. President Donald Trump lashed out at the Iranian nuclear deal this week during a press conference at the White House with French President Emmanuel Macron, calling the agreement “insane” and a “terrible deal,” while warning Iran against restarting its nuclear program if the U.S. pulls out.

“If they restart their nuclear program, they will have bigger problems than they have ever had before,” Trump said, without elaborating further.

For months, U.S. and European officials have been meeting to discuss ways to bolster the Iranian nuclear deal. In January, Trump vowed to pull out of the deal by mid-May, when he must decide to renew sanctions waivers on Iran if it does not address key issues like Iran’s ballistic-missile program.