Sen. Bernie Sanders gave President Donald Trump mixed reviews on foreign policy during a CNN town hall focused on his 2020 presidential campaign on Monday.

Sanders criticized Trump's amiable disposition toward Saudi Arabia, but spoke positively of Trump's efforts to hold dialogue with North Korea.

Trump is traveling to Vietnam this week amid ongoing discussions with North Korean leader Kim Jong Un on the denuclearization of the Korean Peninsula.

Sen. Bernie Sanders of Vermont on Monday went after President Donald Trump for his stance on Saudi Arabia, but spoke positively about Trump's efforts to hold dialogue with North Korea.

During a CNN town hall on Sanders' agenda for his 2020 presidential campaign, the senator was pressured on his stance on the crisis in Venezuela and whether he feels Nicolás Maduro is a dictator.

Sanders stopped short of describing Maduro in these terms, but conceded the country's most recent elections were "undemocratic." The Vermont senator also urged against embracing military intervention in Venezuela, citing the US government's dubious history in Latin America.

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Meanwhile, he questioned why Trump has been so interested in democracy in Venezuela while continuing to be friendly with Saudi Arabia's royal family.

"I do find it interesting that Trump is very concerned about what goes on in Venezuela, but what about the last election that took place in Saudi Arabia? Oh, there wasn’t any election in Saudi Arabia," Sanders said.

Trump continues to face criticism for standing by Crown Prince Mohammed bin Salman, the de facto ruler of Saudi Arabia, following the brutal killing of Saudi journalist and Washington Post columnist Jamal Khashoggi.

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Meanwhile, some in the US foreign policy community are fearful that Trump is leaning toward military intervention in Venezuela against Maduro's socialist government amid the chaos in the Latin American country.

But as Sanders criticized Trump on some issues of global import, he also offered the president some praise regarding his efforts to push North Korean leader Kim Jong Un toward denuclearization.

"I think nuclear weapons in the hands of a brutal, irresponsible dictator is a bad idea," Sanders said of North Korea's Kim. "And if Trump can succeed ... through face-to-face meetings with Kim Jong Un and rid that country of nuclear weapons that is a very good thing."

"I think the idea of going and meeting face-to-face with your adversaries is a good idea," Sanders said.

Read more: In a massive rebuke to Trump, GOP senators demand that Mike Pompeo investigate Jamal Khashoggi's death

In a recent interview with INSIDER, Sanders' foreign policy adviser Matt Duss echoed this view.

"The fact is the US is extraordinarily powerful and we don't have to fear sitting down with anyone, whether it's the North Koreans, whether it's Iran, whomever," Duss said.

Trump is traveling to Hanoi, Vietnam, this week to continue speaking with Kim on the issue of denuclearization after a landmark summit in Singapore last June.