Election Update: Clinton’s Lead Is As Safe As Kerry’s Was In 2004 - Nate Silver [View all]

[RAFisher]

There has been a lot of polling over the past few days in advance of the Republican National Convention, which got underway Monday in Cleveland. But it mostly confirmed the conclusion our election forecast models had arrived at late last week: Hillary Clinton leads Donald Trump by 3 or 4 percentage points. That’s down from a lead of 6 or 7 percentage points a few weeks ago.

As a result, Trump’s odds have improved. He has a 36 percent chance of winning the election, according to our polls-only forecast, and a 38 percent chance according to polls-plus. (While the polls-only and polls-plus forecasts are well aligned now, they may begin to diverge during the conventions — more about that in a moment.)

But Clinton remains ahead of Trump in the clear majority of polls. She leads by about the same margin that Barack Obama did heading into the conventions in 2008, and by a somewhat larger margin than Obama did in 2012.

I’ve nevertheless detected a lot of consternation among Clinton voters: Why isn’t her position safer? There’s really about a 35 or 40 percent chance that Trump will become president?

Based on the polls, we think the model is setting those odds about right. The race is a long way from being a toss-up, but a 3 or 4 percentage point lead heading into the conventions isn’t all that reliable, either. While Obama won twice with pre-convention leads of about that margin, John Kerry went into his convention with a lead of about 3 percentage points in 2004, but lost to George W. Bush. And in 2000, Bush had about a 4-point lead on the eve of the conventions, but lost the popular vote to Al Gore. (Bush won the Electoral College, of course.)

The flip side is that the recent polls could just as easily prove to be a low-water mark for Clinton. Conventions have oftentimes helped the incumbent party’s candidate. One of the biggest turnarounds came in 1988, when Michael Dukakis, the upstart winner of the Democratic nomination, held a lead of 6 or 7 percentage points going into the conventions. But a well-staged Republican convention in New Orleans helped to unify the GOP and highlight the successes of George H.W. Bush and Ronald Reagan, and Bush eventually won by a landslide.

What’s relatively safe to say is that we’ll know a lot more in a month or so. Below, you’ll find a comparison of where national polls stood heading into the challenging party’s convention, and then 30 days after the incumbent party’s convention.1 (By tradition, the incumbent party — Democrats this year — holds their convention last.) The pre-convention polls missed the final margin in the race by an average of 6.4 percentage points. By contrast, the post-convention polls missed it by 4.0 points, a considerable improvement. And since 1972, they’ve gone 11-for-11 in identifying the winner of the popular vote.

Continued on 538:

http://fivethirtyeight.com/features/election-update-clintons-lead-is-as-safe-as-kerrys-was-in-2004/