The 2024 presidential election will kick into yet another gear in the coming days, with the first ballots set to go out in North Carolina on Friday, a debate Sept. 10 and early voting starting in a handful of states shortly thereafter.

The battleground is coming into focus.

There are generally thought to be seven states that are the most in play: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin. But not all swing states are of equal importance. Two — Georgia and Pennsylvania — loom particularly large. It has a lot to do withmath.

Donald Trump’s campaign ad strategy, in particular, appears increasingly focused on these two states. The political data firm AdImpact reported recently that his campaign spent more money in Georgia and Pennsylvania than it did in any other states through late August. According to numbers that AdImpact shared with The Washington Post on Tuesday, these two states also account for more than 81 percent of the Trump campaign’s remaining ad reservations through Election Day.

Pennsylvania ($71 million) and Georgia ($38.8 million) dwarf the other states’ ad reservations, with the third-largest being Arizona ($11.2 million).

Vice President Kamala Harris’s campaign is targeting its war chest more evenly across the seven key states. But apart from the “blue wall” states in the North — Michigan, Pennsylvania and Wisconsin — Georgia is its biggest investment. And Pennsylvania has long been the biggest spending target for both campaigns.

So why are these two states so important?

The most obvious reason is the sheer number of electoral votes available. Among the seven states mentioned above, Pennsylvania (19 electoral votes), Georgia (16) and North Carolina (16) are the biggest prizes.

But it’s also because those electoral votes happen to be just enough for Trump. If he can hold North Carolina — the only one of these seven states he won in both 2016 and 2020 — he probably needs to win only Georgia and Pennsylvania in addition.

Michigan is close behind Georgia and North Carolina, with 15 electoral votes. But, crucially, winning two of the three key states (Pennsylvania, Georgia and North Carolina), plus Michigan, probably would not be enough for Trump; sweeping those three biggest prizes probably would.

The Georgia-North Carolina-Pennsylvania path gets Trump to exactly 270 electoral votes, as long as he holds on to Maine’s 2nd Congressional District, which he won by 10 points in 2016 and seven points in 2020. (Maine and Nebraska are the only states that award electoral votes to the winner of each district. Nebraska’s 2nd District is also in play.)

Here’s how that trifecta would look, courtesy of 270toWin.com. Harris could sweep the rest of the battlegrounds and still lose:

By contrast, if Trump loses one of those three states, he probably needs to win two other states to replace it. So to the extent the Trump campaign is so laser-focused on Georgia and Pennsylvania, it’s something of a high-risk strategy.

Sweeping the three big prizes would also put Harris over the top, at 276 electoral votes. But even if we assume that North Carolina would be a tougher target and stays red, winning Georgia and Pennsylvania means she needs just one more big (that is, not Nevada) swing state.

Here’s how that looks:

Pennsylvania is clearly the biggest prize of all. Both candidates start around 220 electoral votes with all of these races in play (225 for Harris and 219 for Trump). Pennsylvania would account for 42 percent of the electoral votes Harris needs to get to 270; for Trump, it would provide 37 percent.

The Washington Post’s polling average shows Harris leading by an average of three points in Pennsylvania, while Trump leads by two in Georgia. Those are actually among the bigger swing-state margins right now, though all of these states are close and generally within the margin of error in most polls.

That suggests that if Harris can somehow close the gap and win Georgia or Trump could somehow overtake her in Pennsylvania, they would be putting themselves on course for victory.

Just because these are looking like the two key states right now doesn’t mean it will always be the case. If Trump is asserting a real lead in Georgia, for example, you could see the Harris campaign begin to focus more strongly elsewhere. And if Harris is looking stronger in Pennsylvania, you might see the Trump campaign begin to spread the wealth more than its current ad reservations suggest.

But for now, if you want to understand where the presidential race is headed, keep an eye on those two states.