Nate Silver. Screenshot/ABC Renowned statistician Nate Silver on Wednesday revealed his general-election forecast on ABC's "Good Morning America," and he's placing Hillary Clinton at a near 80% favorite to win in the fall.

Silver, who runs the data-journalism website FiveThirtyEight, handicapped Clinton's current odds at 79% while giving Donald Trump a 20% chance of winning the general election.

"We're at halftime of the election right now," Silver said. "She's taking a 7-point, maybe a 10-point lead into halftime."

"There's a lot of football left to be played," he said. "She's ahead in almost every poll, every swing state, every national poll."

He added that "both candidates have a lot of room to grow."

Historically, the last candidate to blow a lead as large as the one Clinton currently holds was former Massachusetts Gov. Michael Dukakis in 1988. Dukakis, who left the Democratic convention that summer with a large lead over then Vice President George H.W. Bush, would later lose by a wide margin in the fall.

"Trump has never been ahead of Clinton in the general-election campaign," Silver said. "He did a great job of appealing to the 40 percent of the GOP he had to win the election, the primary — a lot different than winning 51 percent of 100 percent."

Silver called 49 out of 50 states correctly in the 2008 election and got all 50 states correct in the 2012 election. But earlier this election cycle, he handicapped Trump as having a 2% chance of winning the GOP primary. He later wrote a lengthy piece on how he got the Republican primary race wrong.

FiveThirtyEight launches its general-election forecast later on Wednesday.

Watch Silver's comments below: