There is desperation in Obama’s words.
If Trump were losing, Obama would make the point that Trump is the Republican Party, that he represents the Republican Party, in order to paint the Republican Party as dangerous losers going forward. Instead, obama is arguing that republicans should denounce Trump and that Trump doesn’t represent the Republican Party. In other words, Obama fears that if the Republican Party embraces Trump’s ideas, the democrats have a lot of losing ahead of them in the years to come.
If you’re opponent is a train wreck, you watch and laugh. You don’t try to change their behavior or go out of your way to change an outcome (I.e your opponent losing, and you winning).
The media and the democrats are panicked.