Did Ukraine consent to its own invasion?

Sending troops into a foreign country does not violate international law if that country gave its consent. Is this Russia’s legal justification for its incursion on Ukrainian territory?  According to Bloomberg:

Vitaly Churkin, Russia’s ambassador to the United Nations, said today the crisis is creating serious risks to Russian security and to the safety of millions of Russian-speaking compatriots in southeastern Ukraine. Former Ukrainian President Viktor Yanukovych wrote to Russian President Vladimir Putin requesting a military deployment, Churkin said.

 “It’s completely legitimate under Russian law, and given the extraordinary situation in Ukraine, this threat and the threat to our compatriots, Russian citizens and the Black Sea Fleet,” Churkin told a meeting of the UN Security Council in New York, reading out loud the March 1 letter from Yanukovych.

[Update: and here is Putin: "As you may know, we have a direct appeal from the incumbent and, as I said, legitimate President of Ukraine, Mr Yanukovych, asking us to use the Armed Forces to protect the lives, freedom and health of the citizens of Ukraine."]

It’s a unclear whether Churkin is making a consent argument, a humanitarian intervention argument, a self-defense argument, or all three. But assuming a consent argument is involved, is it valid? After all, Yanukovych was the elected president of Ukraine, and he was never unelected. He was driven out of office after being “impeached” by the Parliament. My understanding is that the impeachment did not follow constitutional procedures. If so, he was removed by a coup. That is, in fact, his view and Russia’s position.

Suppose that is the case. The international law is murky but the rule in these situations is that even when a government is illegally deposed, the successor government inherits its legal authority under international law as long as it controls the territory–the basic idea being that if foreign governments want to trade or otherwise deal with the population, then they must go through whatever entity controls them. There is some doubt about how much the government in Kiev controls the territory, but it certainly exerts greater control over it than Yanukovych does, whose whereabouts are unknown. The new government is also treated as legitimate by many (most?) foreign governments (in contrast to the government that came to power after the controversial coup in Honduras in 2009), and that too contributes to its authority under international law.

Russia disagrees, but even if we therefore conclude that Ukraine currently lacks a legitimate government under international law, it doesn’t follow that Yanukovych, who is now a private citizen, has the authority to invite Russia in. He doesn’t.

And here is Chris Borgen on this topic.