Although why did Trump do it? To look tough? Or could it because he's owned by Putin, and Putin wanted to improve his nukes, but didn't want to break the treaty, but oh look, there's currently a supremely useful idiot/useful supreme idiot at the other side of that treaty. (Too harsh? This is a guy who makes decisions based not on pages of analysis but on what the last person whispered to him)

Geez, you guys are really deep in your conspiracies aren't you? Trumps advisors were plenty warhawks themselves. Remember John Bolton and Pompeo?

They wanted it torn up and there was no secret agenda of Russians involved. The way they justified it was to say that Russia doesn't abide by it anyway, therefore we're just making it official.

But that's just the US perspective. It's possible that Russia was looking forward to it as well, who knows. But in John Boltons book he wrote that the Russians were surprised and he was quite proud of it as well.