Really, I think this is the way to see this. What would Democrats do? They would do what suits the interests of the Democrat party.
I wonder how many times this particular situation has arisen in the recent history of the US -- say since 1900? Situation is (1) supreme court vacancy occurs close to a presidential election (4 months or less before the election), (2) Senate has a narrow majority and is of the same party as the President, and (3) the president appoints and the senate votes BEFORE the new slate of senators/president are inaugurated following the election (for Senators this is early January, for Presidents this is January 21 or thereabout)?