A model from election-forecasting wiz Nate Silver shows Donald Trump once again closing in on Hillary Clinton, as he did right after the party conventions in July, and warned that Clinton's lead is "a lot less safe" than President Obama's lead in the polls in 2012.

Silver's FiveThirtyEight website currently gives Clinton a 58.1 percent chance and Trump a 41.9 percent chance of becoming president.

That's not the closest the two candidates have been, as Silver's widely-respected projection showed them neck-and-neck on July 30. Clinton opened a wider lead over Trump in August in Silver's model, but Trump has been making steady poll gains in September.

Despite Clinton's remaining lead over Trump, several factors should cause Democrats to feel nervous, Silver wrote over the weekend.

FiveThirtyEight's poll average shows Clinton with a 2 percentage point lead over Trump in the popular vote, 46.7 percent to 44.7 percent. But Silver argued she's still less safe than in the close 2012 race between President Obama and Mitt Romney, as Clinton doesn't hold the big swing-state leads Obama did. And, there's a much larger undecided vote this year.

Additionally, the presidential debate Monday evening has the potential to swing polls by 3 or 4 percentage points, enough to put Trump ahead of Clinton in some key states and nationally.

"If the debates cut in Trump's direction instead, he could easily emerge with the lead," Silver wrote. "I'm not sure where that ought to put Democrats on the spectrum between mild unease and full-blown panic. The point is really just that the degree of uncertainty remains high."

A CBS poll released Sunday underscored how the race is tightening in two key states: Virginia and Colorado. Clinton has an 8-point lead in Virginia, although that's down from a 12-point lead last month, according to the survey. And she's just one point up from Trump in Colorado.