Clinton has a 79 percent chance of winning, compared with Trump's 20 percent, according to FiveThirtyEight’s forecast.
"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. She's ahead in almost every poll, every swing state, every national poll."
Silver said "both candidates have a lot of room to grow," but the only recent candidate to blow a lead like the one Clinton holds was Massachusetts' then-Gov. Michael Dukakis in 1988.
"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 states correctly in the 2008 presidential election and got all 50 in 2012.
FiveThirtyEight launches its general election forecast later today here.