Russia doesn’t want Ukraine to be the staging ground for an invasion.

The same Russian propaganda rubbish over and again. No one wants (and wanted) to invade Russia, this is completely out of touch. Russia isn’t afraid of an invasion but of a country like Ukraine (or Georgia, Moldova, the Baltics, and many others) near its borders that strive in a free society. If Russians see there is an alternative state model that gives people a say and hold politicians accountable, it would threaten Russian current dictatorial government. Democracy is Putin’s only enemy.