One of the key security issues facing whoever becomes president in November is the US relationship with Russia.

In the last few years, Russia’s President Vladimir Putin has pushed the envelope on some of the basic principles of international law. In 2014, Moscow covertly occupied, then annexed, the entire region of Crimea. Russia then intervened militarily in other provinces in eastern Ukraine — a conflict that continues, and has so far claimed perhaps 10,000 lives.

In response, NATO has beefed up its presence in member states bordering Russia, out of fear of further aggression. America's response has been tough, but limited by the nuanced nature of Putin’s challenge.

Republican candidate Donald Trump was asked about these issues Sunday in an interview with ABC's George Stephanopoulus.

"He's not going into Ukraine, OK, just so you understand. He's not gonna go into Ukraine, all right? You can mark it down. You can put it down. You can take it anywhere you want.”

Stephanopoulos interrupted to say Putin was already there, and Trump responded: “OK. Well, he's there in a certain way. But I'm not there, you have Obama there, and frankly that whole part of the world is a mess, under Obama."

Trump also told ABC that he was planning to look into the idea of recognizing Russia's annexation of Crimea, and that “from what he'd heard,” the people of Crimea would prefer to be part of Russia.

One of the principles that has governed international relations since 1945 has been that borders cannot be changed by force. Post facto referendums cannot retrospectively legitimize such occupations unless conducted under international supervision. There have been serious questions about the referendums staged by Russia in Crimea — many of the region’s people fled after the Russian occupation.    

In an interview with the New York Times, just before the conventions, Trump said he might not honor America's commitment to NATO allies if invaded by Russia, if they haven't "paid their dues." That has led to widespread anxiety in countries like Estonia and Poland.

Trump has repeatedly said it would be good for the United States to have a strong relationship with Russia.

The Clinton campaign says these remarks indicate that Donald Trump does not appear to know what’s going on in Ukraine or the region.

Questions are also being asked about Trump’s campaign chairman and chief strategist, Paul Manafort, who has worked for pro-Russian political groups in Ukraine for the past 10 years. He also hasd extensive business ties in Ukraine and Russia.

Manafort’s work in Ukraine is the subject of a story in the New York Times, written by Steven Lee Myers in Washington and Moscow correspondent Andrew Kramer.

Manafort’s main client in Ukraine was Viktor Yanukovych. “He tried to sand off some of the rough edges on Yanukovych,” says Kramer. “He was a very Soviet style of politician and with Manafort’s advice he became smoother in his presentation.”

Kramer says Manafort’s role also involved strategy, “advising Yanukovych to exploit wedge issues,” especially ethnic and linguistic divisions in Ukraine, “which is quite a fragile country.”

Yanukovych came to power under Manafort’s tutelage in 2010.

Ultimately Yankukovych and Manafort diverged on strategy, and the Ukrainian leader was later ousted in a violent popular uprising.

Kramer points out it’s not unusual for prominent American politicians to have relationships with powerful businessmen around the world, including in Ukraine and Russia. The Clintons have close ties to some as well.

From PRI's The World ©2016 PRI