Russia is militarily weak but geographically well positioned to threaten NATO's northeast frontiers.
Strategypage looks at post-Soviet Russia's military. It is well worth the read.
Basically Russia has few well-trained troops with decent equipment and a massive land border that requires the threat of nuclear weapons to defend. Russia is weak, with a GDP a tenth of China's and just 6% of America's.
And even Russia's strategic nukes are having money problems despite the priority they have in Russia's battered defense industry. I sometimes wonder if Russian emphasis on shorter range "theater" missiles, done in violation of the Cold War INF treaty, is in part being done to build those simpler missiles to make up for readiness deficiencies in the longer-ranged complex missiles.
Of course, Russia doesn't have to send their army around the world to fight as America must to use it.
And their Finnish, Swedish, Norwegian, Estonian, Latvian, Lithuanian, and Belarusian potential foes (the first two aren't in NATO, with Belarus actually semi-ally of Russia) are very weak while the bulk of NATO power is well to the west and most in North America. Only Poland seems to be more than a speed bump for Russia in the NATO east.
Much like the USSR was weaker than America but only had to advance to the Rhine River to achieve a major victory over NATO, Russia could advance into weakness in the northeast and then dig in, threaten nuclear war if NATO counter-attacks, and hope to hold their gains.
Unlike the Cold War, NATO would not suffer a strategic defeat from such a grab in the Baltics or points north and could take the time to mount a counter-offensive under NATO's own nuclear umbrella.
Luckily for short-term Russian options, Ukraine is a buffer that protects NATO's southeast flank. Ukraine also demonstrates the limits of Russian power. After years of gutting the Ukrainian military and in the midst of a revolution, Ukraine was unable to stop Russia from securing Crimea where Russia already had a major base complex.
Yet Ukraine contained the limited Russian gains in the eastern Donbas. All the talk of novel Russian "hybrid" warfare disguises the fact that Russia was unable to organize a regular smash and grab conquest of eastern Ukraine.
If anyone thinks that Russia chose this diabolical "new" method of warfare and subsequent isolation and sanctions with continued drains on Russian lives and money in an endless low-level war over a rapidly concluded invasion as a superior choice rather than necessity from weakness is deluded.
But then, you know my view on "hybrid warfare" mania.
It really is practically insane* for Russia to needlessly provoke tension with NATO that can't invade Russia (and would rather spend even less on their defense than they do if not for Russian sabre rattling) while ignoring and enabling Chinese military growth in the east where Russian conquests of former Chinese lands might become an active Chinese claim sooner than Russia hoped.
*Although it does make sense if you look at it a certain way.