What Vladimir Putin didn't say may be just as important as what he did say.

In a one-hour speech to a joint session of the Russian parliament, Vladimir Putin did not utter the word "Ukraine" once.

He didn't attack the authorities in Kyiv. He didn't talk about the plight of Russian-speakers in Ukraine. He didn't mention the conflict in Donbas. He did mention Crimea, but only in passing.

This is significant. Along with his live call-in program and his end-of-year press conference, Putin's annual state-of-the-nation address is one of the Kremlin leader's big set pieces.

He has the nation's -- and much of the world's -- attention. It's a valuable opportunity to set an agenda, frame the debate, and lay down markers.

And he chose not to talk -- at all -- about a conflict that has consumed the country and dominated Russia's relations with the West and much of the outside world for the better part of two years.

Just for for a bit of perspective, in his 2014 state-of-the-nation speech, Putin mentioned Ukraine 18 times, including four references in the first five minutes.

Moscow's attention, of course, is elsewhere at the moment.

Russia has a new war in Syria where it is trying to prop up its ally, Bashar al-Assad, while trying -- and largely failing -- to convince the world that it is fighting Islamic State militants.

And the Turkish air force's downing of a Russian SU-24 warplane on November 24 has focused much of the Kremlin's ire on Ankara.

Putin may not have mentioned Ukraine in this year's speech, but he referred to Turkey seven times, Syria eight times, and terrorism 24 times.

Moscow's attention has shifted away from Ukraine because it is losing the conflict in Donbas and losing it decisively.

Putin's Plan A in Donbas, the seizure of what his ideologists call Novorossia -- the strip of land from Kharkiv in the north to Odesa in the south -- was an abject failure.

Most of Ukraine's Russian speakers prefer being an ethnic and linguistic minority in a democracy to being a majority in a kleptocratic autocracy.

And Putin's Plan B, forcing Ukraine to integrate separatist-held territories in the east on Moscow's terms -- as a Trojan horse that can destabilize the country -- is also flailing.

Ukrainian President Petro Poroshenko, who was dealt a terrible hand with the Minsk cease-fire, has played it masterfully.

But the deeper reason Ukraine has faded from the radar -- and from Putin's big speech -- is the underlying logic of policymaking in Moscow.

In a clever piece for the Atlantic Council, Andrew Kornbluth wrote that the Putin regime is not so much a rogue state as a "troll state" that aims to "needle the West and cheer Russians," while at the same time seeking to advance the interests of the Kremlin's ruling clique.

"By tormenting others, trolls create the illusion of action and assuage their own nagging feelings of powerlessness. Likewise, Putin's military adventures in Ukraine and Syria have been remarkably successful at distracting attention from the worsening decay of Russia's human and economic capital," Kornbluth wrote.

"To sustain their short attention spans, trolls must constantly find new and varied ways to bait their opponents. Hence the dizzying pivot from promoting the so-called 'People's Republics' of Donetsk and Luhansk, which were banished from the headlines almost overnight, to heralding the creation of an 'anti-terrorist coalition' in Syria."

But while a foreign policy of trolling can often wrongfoot opponents, it has its limits.

"Trolling can unintentionally escalate into life-or-death confrontation, a risk that was made real when, after months of Russian incursions into foreign airspace from the Baltics to Japan, Turkey shot down a Russian bomber passing over its territory," Kornbluth wrote.

And Russia's trolling adventure in Ukraine has alienated it from the West, led to crippling sanctions, and lost it any vestiges of goodwill in Kyiv, perhaps for generations.

It's no wonder that Putin doesn't want to talk about that.