Or, perhaps a clever trap?
Senators McCain, Graham and now Rubio have come out strongly in favour of Obama's sanctions, leading the call for investigating Russian involvement in the elections. Will be hard for McCain, et. al to back down on this pledge. Hey, and even if the allegations were totally groundless, it's not like there aren't plenty of examples of lengthy congressional investigations based on very little evidence, right?
So, Trump takes office and has a choice. He could stick with Obama's expulsions and not oppose the investigation. But, that would piss the hell out of Putin and the kleptocrats in his own cabinet, who want sanctions lifted pronto and certainly don't want any investigations. I'm pretty sure there's a shit load of stuff they don't want potentially exposed. I can't imagine him sitting on his hands on this one.
Or, he could lift the sanctions, reinstate the diplomats and try to halt the investigation. This is clearly what Putin expects him to do, especially as he's not offering much in the way of retaliation. If Trump does this though, it would send a clear message that his allegiance is to the Russian leadership (either for personal financial gain, they're blackmailing him, or a bit of both) and not the US. His most fervent acolytes will be fine with this of course. But, could widen the fractures within the GOP in congress enough to support the push for Trump's impeachment by the House, then removal by the Senate.
Ball's in Trump's court.