FIRST ON FOX: Sen. Rand Paul, R-Ky., doubled down on his opposition to Ukraine joining the North Atlantic Treaty Organization (NATO), saying it would be an extremely provocative action toward the "pariah nation" of Russia.

Fox News Digital asked the senator on Thursday about his prediction on if or when Russia will invade, to which he responded that no one knows, but that it would be a "great downside" for "pariah nation" Russia.

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"I think nobody knows, I'm still hopeful that they won't invade. I think there's a great downside for Russia. They are already somewhat of a pariah nation, but I think they become more excluded from things, and I think there will be significant repercussions from the Europeans who buy a lot of natural gas from them if they invade Ukraine. So I think they need to know this is not going to, they're not going to get just a pass on this."

Rand Paul on Hannity. (Fox News)

The senator also doubled down on his criticism of Ukraine joining NATO, saying it would likely provoke and anger Russia and isn't the United States' problem to solve. 

"On the other side of the coin, though, I do think it would be good, and it was at least a statement from the Ukrainian prime minister and the German saying there is no imminent call to put Ukraine in NATO. They should have been saying that for a decade or more. It's a dumb idea to put Ukraine in NATO, and it's a very provocative one. I asked the secretary of state the other day, Blinken, I said, ‘What do you think our response would be if Mexico were joining a military alliance with Russia against the United States?’ We would be hopping mad."

German Chancellor Olaf Scholz and Ukraine’s President Volodymyr Zelenskiy said recently that Ukraine's NATO membership is not on the table for the alliance, at the current moment.

United States Secretary of State Antony Blinken speaks as he greets embassy staff at the U.S. embassy, in Kyiv, Ukraine, Wednesday, Jan. 19, 2022. (AP Photo/Alex Brandon, Pool)

These statements come after President Biden and the State Department have expressed support for NATO's "open door" policy when it comes to Ukraine. However, State Department spokesperson Ned Price said during a press briefing recently that it will be up to Ukraine to fulfill membership requirements in order to join the alliance down the road, if the country decides to do so. 

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"So we have to understand that asking countries right on the border of Russia that used to be part of Russia to be in a military alliance against Russia is just a foolhardy idea. Kissinger said this, many others have said this, and I think we should offer them the carrot of that, that they won't be in NATO and at the same time, tell them, though, that if you invade there, the repercussions will be very, very costly and these will be economic repercussions. But all of that requires the cooperation of Europe because we don't buy that much from Russia," Paul told Fox News Digital.

Henry Kissinger, the former secretary of state and national security advisor under Presidents Richard Nixon and Gerald Ford, held similar views as the Kentucky senator.

WASHINGTON, DC - MAY 11: U.S. Sen. Rand Paul (R-KY) questions Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, during a Senate Health, Education, Labor and Pensions Committee hearing to discuss the ongoing federal response to COVID-19 on May 11, 2021 in Washington, D.C. (Greg Nash-Pool/Getty Images)

In a recent op-ed, Paul points out that Kissinger advised that Ukraine should remain neutral to survive due to its geographical location. Kissinger previously wrote, "For Ukraine to survive, "it must not be either side’s outpost against the other — it should function as a bridge between them."

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Paul threatened on Thursday to block a quick passage of the Senate resolution pledging support for Ukraine. The resolution required unanimous consent, meaning every senator had to agree in order to pass it in a timely manner.

"We have some amendments to it. We believe that it should say nothing in this resolution is to be construed as an authorization of war and nothing in this resolution is to be construed as authorizing the use of troops into Ukraine," Paul reportedly said

Paul's amendment, that nothing should be construed as a declaration of war, was accepted and included in the resolution, which passed Thursday evening.