Is this not giving Trump and Putin a big red button stand off?
No. This is hardly the first time the USA has expelled Russian diplomats, nor is it the biggest expulsion. Obama expelled 2 Russian diplomats in July. George W Bush expelled 50 Russian diplomats in 2001 over the Robert Hanssen spying case. Indeed, countries expelling each other's diplomats happens a lot without the countries going to war, or even going to the brink of war. It heightens the tension between the USA and Russia a little but it is a long way short of a red button stand off.
Given the evidence of Russia's attempt to influence the outcome of the presidential election this action is entirely understandable and, in my view, justified. History tells us that appeasing people like Putin always ends badly. He needs to know that he cannot do whatever he wants.
Unfortunately Trump does not want to accept the evidence of Russian interference and his statements about Putin so far suggest he is more inclined to appease (although a recent tweet suggests a possible change of heart). That is far more worrying than Obama expelling 35 diplomats.