Obama is attacking those Republicans who do not support Donald Trump just as viciously, if not more so, as he attacks Trump himself and those who support Trump.

The N.Y. Times reported on October 24, 2016:

President Obama on Sunday savaged Representative Joe Heck, Republican of Nevada, for failing to reject Donald J. Trump earlier in the presidential race, seeking to tarnish Mr. Heck and other Republican candidates across the country by association with a standard-bearer he called indecent and unfit for the presidency.

If the Republicans who abandoned Trump thought they would get praise from the Democrats and weak opposition to their elections, they were wrong.  Nobody, especially Obama, has any respect for those who abandon their party's nominee during an election.  Democrats fight to win.  Unlike Republicans, no Democrat has abandoned Hillary or criticized her because of her Emailgate scandal, or Benghazi, or pay to play, or anything else.  The Democrats are solidly behind Hillary to win.  They attack any Republican regardless of whether he endorses or doesn't approve of Trump.  Republicans who attacked or abandoned or refused to endorse Trump do not receive any dispensation from Democrats, especially Obama on the campaign.

Obama and his wife, Michelle, are spending more time campaigning for Hillary that Hillary is herself.  Hillary is resting, and allowing Obama and Michelle to act as her attack dogs, a role typically for the V.P. nominee.  Obama is campaigning furiously to protect his legacy by helping Hillary win, because he knows that Trump will get rid of Obamacare, secure the border, end federal money to sanctuary cities, cancel the Iran appeasement deal, reduce tax rates, and re-negotiate trade deals.  These are the opposite of Obama's policies, and a repudiation of the Obama legacy. 

 Obama must also fear a Trump victory that would lead to an Independent prosecutor to investigate the Hillary Emailgate scandal because he, Obama, knew that Hillary was using a non-secure private email system, and his State Department asked the FBI to reclassify a confidential email.  Obama denied that he knew that Hillary was using a private non-secure system and said he learned about it when the media reported it about March 15, 2015.  The Podesta emails show that Obama knew before it was reported by the media.

The polls would be much closer if all Republicans, such as Kasich, Romney, Thune, Ryan, McCain, the Bush clan, Flake, Toomey, Fiorina, and others united behind the nominee chosen by the primary voters.  These Republicans have done a disservice to the Republican primary voters and Trump by refusing to help Trump.  The refusal to help Trump is also a repudiation of the wishes of the primary voters.

Obama, speaking for Democrats, mocks and attacks these Republicans because they did not repudiate Trump quickly and early enough to satisfy Obama.  Obama wants total surrender from these Republicans.