Pence said it's "very disappointing" to see Obama break with the tradition of former presidents, who largely shun the campaign trail, and "become so political".
Obama's office announced his first round of endorsements earlier this year and the official said his second round will be released in coming weeks.
Former US President Barack Obama participates in a political rally for California Democratic candidates during a event in Anaheim, California, US Saturday.
Obama warned that the country is at "one of those pivotal moments when everyone of us as citizens of the United States needs to determine just who it is that we are".
Mr Trump is "just capitalising on resentments that politicians have been fanning for years", the former president said.
Pence says Obama rolled out "the same exhausted arguments that he and liberals have made over the last eight years". "I found he's very good for sleeping", Trump said at a campaign appearance in Fargo, North Dakota.
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While Obama has in the past blasted Trump and his policies , this was the first speech in which he used his successor's name. Obama , himself, acknowledged that his critique of President Trump was something of a deviation from tradition.
"It should not be a partisan issue to say that we do not pressure the attorney general or the Federal Bureau of Investigation to use the criminal justice system as a cudgel to punish our political opponents", he said, a reference to Trump's demands. "In 2 months, we have the chance to restore some sanity to our politics". In the other Orange County race, Gil Cisneros, a Democratic philanthropist and Navy veteran, is vying for an open seat created by retiring Republican Ed Royce.
Here was one of Obama's salvos during his speech: "Sometimes the backlash comes from people who are genuinely, if wrongly, fearful of change", he said.
Lamenting the current political climate, Obama said that Trump was a "symptom, not a cause".
"For three cycles President Obama fired up Republicans like nobody and I'm happy if he wants to do it again", he said at a Christian Science Monitor breakfast in Washington. "It is us not doing what we're supposed to do", he said.
The Republican National Committee, for its part, responded to Obama's speech by saying, "President Obama stepped back into the spotlight to make the case that our country is on the wrong track".
"By the way, that claim that everything will turn out OK because there are people inside the White House who secretly aren't following the president's orders?"
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Obama touted his own administration's record in the aftermath of the Great Recession and rebuked Republicans for calling job growth and economic expansion now a "miracle".
He criticized Republican efforts to curb or remove laws involving voting rights, campaign finance limits and the social safety net while backing tax cuts and embracing "wild conspiracy theories", including one once endorsed by Trump - that Obama was not born in the U.S.
At 12 p.m. EST today, former President Barack Obama is expected to kick off his push to help Democrats in the 2018 midterm elections.
He said everyone needed to vote irrespective of their choices because that was what democracy depended on to thrive.
In a speech at the University of IL at Urbana-Champaign, Obama said Americans were living in "dangerous times" and accused Republicans of undermining global alliances, cozying up to Russian Federation and exploding the federal deficit.
Speaking about the Democrat campaign, Mr Obama said to loud cheers: "We're going to put on our marching shoes, we're going to start knocking on some doors, we're going to start making some calls".
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The entire speech can be viewed below, live at Noon EST.