Clinton 2016 campaign manager cautions against exit polls: 'They may break your heart'

Robby Mook, the former campaign manager for Hillary ClintonHillary Diane Rodham ClintonDemocrat Katie Porter unseats GOP's Mimi Walters Former Facebook security chief: 'I failed to prepare my employer' on Russian disinformation Rand Paul: Facebook must 'convince conservatives they're not the enemy' MORE's 2016 Democratic presidential bid, cautioned ahead of Tuesday's midterms to treat exit polls "like online dating profiles."

"Things may not be as they appear. And they may break your heart," Mook wrote on Twitter.

Mook's warning came as results began trickling in from initial exit polls early Tuesday evening.

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A preliminary CNN poll showed that 44 percent of voters approve of President TrumpDonald John TrumpAvenatti ‘still considering’ presidential run despite domestic violence arrest Mulvaney positioning himself to be Commerce Secretary: report Kasich: Wouldn’t want presidential run to ‘diminish my voice’ MORE's job performance, while 55 percent disapprove. The same initial exit poll found two-thirds of voters said Tuesday's vote was about Trump's presidency.

An Associated Press survey conducted with NORC at the University of Chicago found that health care and immigration were the two most important issues to voters in Tuesday's midterm elections.

Each of those preliminary results were released before the first polls closed across the country, and are therefore subject to change. Democrats are seeking to retake the majority in the House and Senate in Tuesday's elections. Political forecasters give them a strong chance of retaking the lower chamber.

Exit polls in the 2016 presidential election showed Clinton with a lead over Trump, and prognosticators heavily projected that the Democratic nominee would prevail.

But Trump ultimately won the Electoral College, 304-227, but lost the popular vote by nearly 3 million votes.