He's not - and never has - condemned or opposed it either though; I think the US may have dodged a bullet with not re-electing Trump, because if he used his position as supreme commander to not act on Russia's aggression (which he would be required to due to NATO etc), it would destabilize NATO and make it a toothless tiger. He's always been a fan of Putin, and especially early on during his presidency there were accusations and rumors of him being in Putin's pocket (via extortion, 'kompromat', but given the quotes over the years I don't think that would have been necessary).

A selection of quotes: https://edition.cnn.com/2016/07/28/politics/donald-trump-vla...