The pattern you're looking for is "when I have an asset in the White House, I don't need to waste huge amounts of resources and global credibility on a stupid and brute military campaign, I can just use the asset."
Also perhaps "when I have an asset in the White House, I should not undermine his local image with a power struggle".
While you're wondering, consider the possibility that Russia had more convenient means than military force for achieving its policy goals during the Trump administration.
Then while you're specifically considering Crimea, consider which US president simply said "Oh yeah, Crimea is russian":
Nevertheless, if Ukraine was a thorn in the Kremlin's side, or at least a potential trouble source, it would have been rational for Russia to stabilize the issue with an invasion during a friendly US admin, rather than leave the situation uncertain, and then have to resolve it against the type of US admin such as exists today.
That strategic decision cannot be explained by your theory, discredited media stories notwithstanding.
If Ukraine was THE thorn in the Kremlin's side... vs one point in a constellation of concerns including undermining NATO [0], weakening the EU [1], weakening the US, affirming nationalist authoritarianism vs social democracy, etc etc.
> it would have been rational for Russia to stabilize the issue with an invasion
If invasions didn't have any risks and consequences (even absent US intervention). And at this point, it sure looks like those risks and consequences are on full display even if we only look at the military action.
Meanwhile 3 years ago it actually looked plausible that the US could be forced into having to sacrifice either aid to Ukraine or the candidate that eventually beat Trump.
> discredited media stories notwithstanding.
"discredited" needs citation. Especially considering that the introductory set of articles I linked to above isn't even the short list.
Also perhaps "when I have an asset in the White House, I should not undermine his local image with a power struggle".