The US President has faced a backlash from his critics after signing an executive order temporarily barring citizens from seven mainly Muslim countries.
Mr Trump insists the policy is not a ban on Muslims but was instead “vital” in the fight against terrorism.
The Republican has vowed to fight a federal judge’s nationwide block on the order, hinting he could even create a new ban.
Bernie Sanders said Donald Trump's travel ban was based on 'racism'
There’s a whole lot of discussion about the racist immigration policies of the Trump administration
But, the senator, who challenged Hillary Clinton for the Democratic presidential nomination last year, railed against the ban insisting the US already had “very strong” vetting mechanisms in place for vetting migrants.
Mr Sanders told NBC: “If anybody has an idea of how we can make them stronger let’s go forward.
“I don’t think there is any debate that we want to keep the United States safe and we want to be 100 percent clear that anybody who comes into this country should not be coming into this country to do us harm.
“There’s a whole lot of discussion about the racist, in my view, immigration policies of the Trump administration which are based on anti-Muslim ideology.”
The senate said the US already had "very good" vetting mechanisms
In the heated interview, the 75-year-old also took aim at the president for his allegations of illegal voter fraud in November’s election.
“We have a president who is delusional in many respects, a pathological liar,” Mr Sanders continued.
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“When somebody goes before you and says that 3 to 5 million people voted illegally… nobody believes that.
“There is not a scintilla of evidence to believe that, what would you call that remark? It’s a lie. It’s a delusion.”
Donald Trump has faced criticism for his executive order
The suspension of Mr Trump’s immigration order was upheld by the Court of Appeal on Friday.
The US President says he intendeds to create a new executive order on immigration within days.
He told reporters on Air Force One that a new order would have very few changes and indicated that it may be signed as early as Monday or Tuesday.
On Sunday, the White House’s policy advisor Stephen Miller, who played a key role in drafting the legislation, also attacked the judiciary branch of America.
He said: "A district judge in Seattle cannot make immigration law for the United States.
"The administration is pursuing every single possible action to keep our country safe from terrorism."
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