Robby Mook, the former campaign manager for Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college 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.

Warning: exit polls are like online dating profiles. Things may not be as they appear. And they may break your heart. — Robby Mook (@RobbyMook) November 6, 2018

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 Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate 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.