Last Monday, I wrote that “If Obama’s four point lead persists through the week, Obama should be considered a very strong favorite for reelection.” The last week has come and gone, and Obama retains a four-point advantage nationally. This argument will be elaborated on over the course of this week, but the bottom line is that Obama’s a heavy favorite for reelection.

In post-convention polls, Obama holds an average of 49 percent of the vote and leads by about 4 points. The president holds a broad advantage across the battleground states, including modest leads in Ohio, Virginia, and Wisconsin. Polls released on Friday and over the weekend were consistent with this assessment: The Gallup approval tracker jumped in Obama’s direction on Sunday; the RAND American Life Panel shows Obama securing his largest lead to date with nearly 50 percent of the vote; the highly regarded “Ohio Poll” conducted by the University of Cincinnati showed Obama up five in the Buckeye State, and a wave of Purple Strategies polls pointed toward a broad Obama lead across the battleground states.

While Obama’s 4-point lead is very modest by historic standard, it’s larger than it sounds. Only a sliver of voters are remain undecided and Obama holds approximately 49 percent of the vote, suggesting that Romney will need to fare exceptionally well among the remaining undecided voters and then further count on either low-Democratic turnout or Obama supporters switching sides. All of these scenarios are possible; none are likely. Obama is a well-known incumbent president and voters have hardened impression of his performance, as demonstrated by the stability of the race and his resilience in states where he faced months of uncontested advertisements, like Michigan, Minnesota, or New Mexico. Battleground state voters have already heard a whole presidential campaign’s worth of advertisements, suggesting that a deluge of late spending is unlikely to change the outcome. The possibility of a late swing is further reduced by the rise of early voting, as nearly one-third of voters are expected to cast ballots before Election Day.

Most assume that the heart of the race is still to come, but history suggests that most voters have made up their minds by this stage. Every candidate with a clear lead in the late September polls has won the popular vote in the last fifteen presidential elections since 1948. The debates, for instance, simply haven’t played the decisive role suggested by campaign lore. In fact, most of the biggest late movements in modern presidential history aren’t even associated with the debates, like 1948 or 1968 when there weren’t debates at all. In 1976, Ford mounted a late comeback in spite of a debate performance that included the ludicrous assertion that there was “no Soviet domination of Eastern Europe.” With the exception of Reagan-Carter, the elections with late movement involved unusual incumbent-party candidates who ascended to the presidency or the party’s nomination following the death, resignation, or decision not to run by an incumbent president. That’s probably not a coincidence.