Dukakis beat out Bruce Babbitt, former governor from Arizona; Joseph Biden, senator from Delaware; Dick Gephardt, representative from Missouri; Al Gore, senator from Tennessee; Gary Hart, former senator from Colorado; Jesse Jackson; and Paul Simon, senator from Illinois and pop singer. Okay, that last part was a joke.
Hart was originally a front runner in polls. But his campaign collapsed when he was discovered having an ongoing affair with a woman named Donna Rice.
Biden’s campaign collapsed when it was found he had plagiarized his announcement speech. And it was the Dukakis campaign staff that leaked the evidence of this to the press and gained a double windfall; Biden was knocked out and, at the time, the Gephardt campaign was blamed for the leak.