Colorado Sen. Cory Gardner is taking a hard line on North Korea after talks between President Donald Trump and North Korean leader Kim Jong Un suddenly broke off Thursday when Kim refused to agree to fully dismantle his nuclear weapons program.

Gardner, a Republican who chairs the Senate’s subcommittee on East Asia, called Kim a “two-bit dictator” and said the US must keep full economic sanctions against Kim’s regime.

Gardner authored a broad sanctions policy against North Korea that became law during President Barack Obama’s administration.

The senator has been cautiously supportive about Trump’s past efforts to negotiate directly with Kim, though he was sharply critical Thursday.

“Kim Jong Un is a two-bit dictator who will always put his own interests and the preservation of his neo-Stalinist regime ahead of the basic human rights of the people of his country,” Gardner said in a statement.

“North Korea continues to be a nuclear threat to the United States and our allies and every time we have tried to negotiate in good faith with this regime, it led to a shakedown – pure and simple,” he said.

During Trump’s first negotiations with North Korea, he agreed to stop joint US-South Korea military exercises – a decision that was criticized by Republicans and Democrats alike.

Gardner said US law requires that the goal of any negotiation with North Korea must be to end its nuclear weapons threat.

“Until then, we must pursue the policy of maximum pressure,” he said.