Will Russia invade Ukraine?
Could Russia intervene militarily in Crimea to safeguard its strategic interests? Or, to put the question a different way, has Russia already intervened?
Nobody yet knows the identities of the armed men who seized control of Simferopol airport.
But their equipment, their vehicles and their behaviour all signal that this is a trained military unit, not a rag-tag group of pro-Russian loyalists.
"These men look like a formed and organised body of troops. They appear to be disciplined, confident and uniformly dressed and equipped," says Brigadier Ben Barry, a land warfare expert at the International Institute for Strategic Studies in London.
"Irregular militia may obtain bits of official kit but they tend to look like a military jumble sale."
All we know is that what looks to be a military unit has secured the airport in Simferopol, the Crimean regional capital.
This comes against a background of deepening tensions, with the Russians working through a predictable play-book of threats and menaces aimed at the new interim authorities in Ukraine.
Combat aircraft in areas bordering Ukraine are on alert. Snap military exercises have been held to demonstrate the readiness of Russian forces.
There have been economic threats too, for example to increase customs duties at the two countries' border along with widespread rhetoric warning of the threats to Russian minorities, orthodox religious shrines and so on.
So far, it looks much like the preliminaries to the Russian assault on Georgia back in 2008.
Then, of course, the Georgian military did the Russians the favour of moving first into the separatist enclave of South Ossetia sparking a furious Russian response.
But comparisons can be misleading.
Georgia was a small country that had deeply irritated Moscow and one that could do little to respond against Russia's overwhelming military might.
Many experts believe a similar full-scale Russian intervention in Ukraine is unlikely.
Given the size of Ukraine and the divisions within its population, it would simply saddle Russia with involvement in what might rapidly become a bitter civil war.
Russian pressure at the moment serves a different goal.
Ukraine is heading towards bankruptcy. It needs outside funding. Moscow knows that Western financial institutions must play some kind of role.
Its concern is to underline in as clear terms as possible that any future Ukrainian government should tilt as much towards Moscow as it does to the EU.
Russia's bottom line is that Kiev should resist any temptation to draw towards Nato.
Crimea though is another matter. For a start the Russian military does not need to invade - it is already there, leasing facilities from the Ukrainian authorities.
The bulk of Russia's Black Sea Fleet is based in Crimea with its headquarters in Sevastopol.
Russian naval personnel come and go in Sevastopol as if it were a Russian city. The navy dominates the town.
While largely made up of naval personnel, the Black Sea Fleet also has a contingent of marines and there have been a series of reports suggesting that Russian forces in and around Sevastopol have been bolstered in recent days.
Crimea has a very large pro-Russian population, who are probably in the majority.
Many Russian naval personnel have retired there - and it is distanced physically and politically from Kiev.
Russian pressure in Crimea again serves Moscow's wider purpose of reminding Ukraine's new rulers that Moscow's concerns must be considered in any future economic and diplomatic arrangements.