Tuesday night we saw what happens when polls are uniformly biased against a party that’s favored to win nonetheless. Those polls get aggregated, aggregators project the likeliest outcome, and the winning party beats that projection. Before the returns came in, the overwhelming consensus was that Republicans would win the Senate, but with a one- or two-seat majority. In the end, it looks like their margin will be four.

This says less about the merits of poll aggregating than narrative-driving pundits would have you believe. But the error was nevertheless profound. The practical differences between a 51-seat GOP majority and a 54-seat GOP majority are tremendous. And the person who should be most concerned about the difference is Hillary Clinton.

The most conventional, but also most well-grounded, assumption before Tuesday night was that Republicans would win a narrow, and thus short-lived, majority. As late as 9:36 p.m. last night, conservative writer Tim Carney wrote a short article headlined “Tonight’s darker omen for the GOP: Losing the Senate in 2016.”

At the time, the logic was unimpeachable. Republicans would enter the presidential election cycle with a paper-thin majority, and too many vulnerable incumbents to defend.

With 54 (likely) members, Republicans don’t by any means have an unbeatable majority. But for Democrats to make Mitch McConnell a one-term majority leader, they can no longer count on the 2016 map to do it for them. They’ll need the turnout pattern of the last six years to repeat itself one more time, and propel Democrats to victory basically everywhere.

That presents Clinton with an immense burden. Yesterday the best bet in politics was on a Clinton presidency, a Democratic Senate and a Republican House. Today, it might be on a Clinton presidency and a Republican Congress. Whereas one day ago, Democrats had decent reasons to believe they could recapture the Senate even if Republicans won the White House in 2016, today, they must know that if a Republican wins the presidency, his party will control the entire government.

The practical differences between Clinton presiding over a divided Congress and a fully Republican Congress aren’t great. The possibility that she’ll be negotiating with two Republican houses instead of one shouldn’t deter her or discourage any Democratic presidential hopeful.

To the contrary, the GOP’s big showing yesterday ought to in some ways excite Clinton. An emboldened Republican Party is likelier than a one-vote majority to overreach, as it did in 2011, and set itself up for an unflattering contrast two years from now.

Likelier, but not guaranteed. Republicans could just as easily figure out to behave. If they do, Clinton's margin for error will be vanishingly small. No Democrat wants to lose the election that returns to power a Republican Party that has grown significantly more reactionary since they last controlled the government under George W. Bush. But those are now the stakes.