Speaking to reporters after a briefing on the Orlando shooting, Obama said Trump’s call for tougher talk on terrorism and a strict ban on Muslim immigration would make Muslim Americans feel betrayed by their government and would undermine American values.

“If we ever abandon those values, we would not only make it a lot easier to radicalize people here and around the world, but we would have betrayed the very things we are trying to protect.” Obama said. “And then the terrorists would have won and we cannot let that happen. I will not let that happen.”

The president’s remarks were his first reaction to Trump’s speech Monday after Sunday’s mass shooting — and perhaps his strongest yet on the threat he sees the businessman candidate poses to the U.S. politics and security.

Obama said Trump’s plan to bar foreign Muslims from entering the U.S. ignored America’s history of targeting ethnic and religious groups amid period of anxiety.

“We’ve gone through moments in our history before when we acted out of fear and we came to regret it,” Obama told reporters. “We’ve seen our government mistreat our fellow citizens and it has been a shameful part of our history.”

“Where does this stop?” he said.

Obama directly addressed a specific critique lodged not only by Trump, but by other top Republicans, that his counterterrorism efforts have been hampered by his refusal to use phrase “radical Islam” when describing the forces urging attacks like the one in Orlando.

Obama called that criticism a “political talking point.”

“There’s no magic to the phrase ‘radical Islam,'” he said. “If someone seriously thinks we don’t know who we’re fighting, if there’s anyone out there who thinks we’re confused about who our enemies are, that would come as a surprise to the thousands of terrorists we’ve taken off the battlefield.”

Obama argued that treating Muslim Americans differently makes the country less safe by fueling the notion among followers of the Islamic State group that the West hates Muslims.