The Clinton team’s decision to focus so much more attention on states that it wants to win—as opposed to those it believes it needs to win—represents one of the central, if often unremarked upon, choices of the 2016 election. It has allowed her to play offense for most of the general election, while forcing rival Donald Trump to spend most of his energy defending states more indispensable to his strategy than to hers.

But it’s also meant Clinton has devoted little attention, beyond field organizing, to fortifying states where Trump is now making a late push amid the tailwind of tightening national polls. With Trump consolidating traditional Republican voters, Clinton faces the risk that she has overestimated her hold on the places most central to her strategy.

Put another way, as Clinton has focused her time and money primarily on swing and Republican-leaning states, the question looming over her campaign is whether she has left herself open to a flanking maneuver from Trump in any of the seemingly safe Democratic states that he is now targeting—key among them Colorado, Michigan, and Wisconsin. “For a Republican nominee to breach the ‘blue wall’ of Wisconsin and Michigan, they need to invest in those states and hope for a national tide to come in,” said Brent McGoldrick, the co-founder of the Republican voter-targeting firm Deep Root Analytics. “It’s possible she left herself open to that breach.”