Donald Trump campaign chair Paul Manafort resigned Friday, the latest in a series of shakeups this week at the top of the campaign. Now the Trump team has booked TV ad time in swing states and the GOP nominee has struck a new tone with speeches over the last few days.

But the last few weeks have been good for Democratic nominee Hillary Clinton.

Clinton leads Trump in national polls and more importantly, in key states. The states that are traditionally where campaigns are won and lost are mostly leaning heavily in her direction. Since last month’s conventions, Clinton has taken double-digit leads in enough states to win the presidency. Her campaign is spending tens of millions of dollars on TV ads, while the Trump campaign general election advertising blitz is just beginning.

The timing of her advantage is important. That’s because voting in the 2016 presidential election begins sooner than you might think. In Massachusetts, we’re used to thinking of voting as the thing we do on that Tuesday in November — when we trudge to our designated polling place to cast our ballots. But in 37 states, now including Massachusetts, some form of early voting will start sooner than that. In some states, early voting is just over a month away.

More than a majority of states allow for early voting in some form. (Courtesy National Conference of State Legislatures)

According to the U.S. Census, nearly a third of voters nationwide cast early ballots in 2012, and that number could go higher this year. In some states, more than half of votes are likely to be in before Election Day.

This wrinkle in campaign timing adds significance to Clinton's current advantage and urgency for Donald Trump’s campaign. Early voting gives an advantage to the campaign in the lead even well before Election Day arrives. If Clinton is still riding high as we move through September, she will start racking up votes, not just favorable news cycles. Her early advantage represents an opportunity to turn a lead in the polls into a lead in real votes even before Election Day arrives.

This week’s staff shakeup in the Trump campaign may be helpful, but the window to really turn things around is closing. And Trump's campaign is lagging behind Clinton’s in important ways. Early voting favors candidates with sophisticated turnout operations and modern data and analytics. Knowing things like where your supporters are, who is likely to vote early and who has voted already are all critical. By all accounts, the Clinton campaign is far ahead of Trump in building modern data infrastructure.

Time is running short for Trump to catch up. Once voters begin casting their ballots, improving poll numbers become less valuable with each passing day. Persuading voters does no good after they have cast their ballots.