Lindsey Graham. AP Photo/Jim Cole Top Republican Sen. Lindsey Graham, a vocal critic of Donald Trump throughout the election cycle, slammed the president-elect's views on foreign policy in a wide-ranging interview with Business Insider last week.

He called Trump a "fool" when it comes to Russia, said the billionaire businessman has "zero idea" about how to defeat the terrorist group ISIS (also known as the Islamic State or ISIL), called his views on the NATO alliance "dangerous," and said Trump "doesn't know anything" about foreign policy writ large.

"To put 'Donald Trump' and 'foreign policy' in the same sentence is a stretch," Graham said. "This is not his area. He doesn't know anything about it. He doesn't seem to be curious."

Regardless, Graham, who ran for president himself during the Republican primary, will have to work with Trump in his coming administration. We've outlined what Graham thinks foreign policy will look like under President Trump.

Russia, Syria, and Iran

Graham seemed especially concerned about Trump's views on Russia.

"I think [Trump's views on Russia] are the biggest misreading since the '30s and Donald Trump is a fool when it comes to Russia," he said.

During his campaign, Trump was often criticized for warming up to Russian President Vladimir Putin, who had spoken favorably of the then-Republican presidential nominee.

"I think Russia would love for him to win," Graham said. "The fact that the Russians are actively involved in this election says all I need to know about Donald Trump. I've never, I can't believe I’ve lived long enough to see a foreign government this involved in our election."

The US accused Russian hackers of leaking emails from the Democratic National Committee, and the Kremlin has apparently hired Russian internet trolls to pose as pro-Trump Americans.

Russia might have a particular interest in US politics as it seeks to expand its power throughout the world.

Russia is involved in the Syrian civil war, a conflict the US is also entangled in, and the Kremlin backs a dictator whom the US has insisted must leave power. Russia is also closely aligned with Iran, which is involved in the Syrian conflict as well as the fight against ISIS in Iraq. But Iran's militias have been accused of committing atrocities against Iraqi civilians as they help liberate towns and cities from ISIS control.

Trump has suggested that Syrian President Bashar Assad should be able to remain in power and help the US fight ISIS in the Middle East — which is exactly what Assad, who wants to be viewed as a legitimate partner in the fight against terrorism, wants to hear. But his regime has killed far more civilians in Syria than ISIS, and he has shown that he’s more interested in wiping out the moderate rebels who oppose his regime than the Islamist terrorists who are seeking to control parts of the country.

"To suggest that it's OK to leave Assad in power, you have no idea what that means for the Mideast," Graham said. "That means every Arab government is going to rebel against that decision because to give Assad, to keep him in power is giving Damascus to the Iranians, and you're not going to do that. That means empowering the Russians in a way that we haven’t seen since the '70s."

Iran, a hardline Islamic country with strong anti-American sentiment, is on the side of the Assad government in Syria. Foreign policy experts often express concerns about Iranian influence in the Middle East.

Graham predicted that some Republicans in Congress would resist Trump's policies on Russia.

"There will be people in the Congress on the Republican side who push back," Graham said. "I will gladly work with him where I can."

Trump hugs a U.S. flag as he comes onstage to another rally with supporters in Tampa, Florida on October 24. REUTERS

NATO

Graham also bashed Trump's comments on NATO, an alliance that was formed in 1949 to counter the Soviet Union and nationalist militarism in Europe.

Trump has said that NATO is "obsolete" and suggested that, under his administration, the US might not defend its allies if those allies didn't contribute enough to their own defense.

"What he's saying is very dangerous," Graham said. "He's diminishing alliances at a time when we need more. Yes, NATO members need to contribute more. But this is not a country club where you get kicked out if you don’t pay your dues. This is not a real-estate deal where you leverage for the best price. This is a complicated world where alliances, imperfect as they are, have to be nurtured and built up."

This is another area in which Trump sides with Russia, which is not a member of NATO.

Russia has reason to hope the alliance crumbles — it's one of the biggest checks against Russian expansion of power. NATO includes 28 member countries and serves, among other things, as a counterweight to the Kremlin's ambitions in Eastern Europe.

Several post-Soviet states, including Lithuania, Latvia, and Estonia, are NATO members. And if Russia were to attempt to invade any of them, the US would be obligated to throw its military might behind counteracting the Kremlin and defending those countries' sovereignty.

"Russia has to be very excited about Donald Trump's view of NATO," Graham said.

A Kurdish fighter from the People's Protection Units (YPG) carries his weapon as he walks at the faculty of economics where a defaced picture of Syrian President Bashar al-Assad is seen in the background, in the Ghwairan neighborhood of Hasaka Thomson Reuters

ISIS

The fight against ISIS in the Middle East was a top issue on both sides throughout general election campaigning.

Trump often advocated for letting Russia and the Assad regime help the US defeat ISIS in Syria and bombing "the hell out of ISIS" in other parts of the Middle East where ISIS controls territory. He has also suggested that the US take ISIS' oil to deprive the terror group of one of its largest sources of revenue.

But Graham said this strategy is flawed, noting Trump's rhetoric that could be perceived in the Middle East as anti-Muslim. During his campaign, Trump proposed barring all Muslims from traveling to the US "until our country's representatives can figure out what is going on" with terrorism.

"He has zero idea about how to defeat ISIL, because you've got to hold the territory," Graham said.

So far, Trump has not articulated a plan for establishing security in areas liberated from ISIS. During the Iraq War, the US and its allies in the Iraqi government wiped out Al Qaeda in Iraq, the predecessor to ISIS, in most of the country. But the group then went underground and reemerged later as an even more powerful and formidable enemy.

Graham argues that Trump’s rhetoric might make it difficult for Muslims in the Middle East to see the US as an ally, thereby hurting America's ability to stem ISIS recruitment and establish security in the region post-ISIS.

"If anybody understood the war on terror at all, the last thing he would do is make the statement 'we need to ban all Muslims from coming to America,'" Graham said. "Because what you're doing is you're empowering the enemy."

He explained: "What you're doing is you're empowering the enemy. The enemy's narrative is that the West hates the religion. Our narrative should be that … that it's the world against ISIL, not the United States against Muslims."