If Hillary Clinton is sworn in as the 45th president of the United States this January, she has committed that right out of the gate she will push hard to reform our immigration system, protect the rights of marginalized groups, and more. But how much Clinton would be able to accomplish hinges on the political landscape she faces in the Senate. In many ways, it’s a tale of two presidencies.

In one future, a President Clinton could work with a Democratic Senate to confirm an administration staffed with excellent people dedicated to pushing a clearly-articulated agenda to move the country forward. In this future, her qualified choices for top jobs in the administration get approved: our secretary of labor is a champion for the rights of low-wage workers and our attorney general is committed to a justice system that treats all Americans equally. Across the board, capable executive nominees are able to carry out the administration’s vision for progress.

The same could go for judicial nominations. With Democrats controlling the Senate, we could dig out of the huge backlog of judicial nominees at every level that has been created by years of unprecedented Republican obstruction. From district courts across the country to the highest court in the land, a Democratic Senate would allow Clinton to get judges confirmed who respect the Constitution -- and who believe it’s there for all Americans, rather than just the rich and powerful.

By contrast, the other possible future would be bleak. That future, in fact, may look a lot like the recent past or worse, as Republican leadership and rank-and-file members dug their heels in -- literally from day one -- against everything President Obama tried to take on. If you thought it was bad under President Obama, it could get even worse as the base looks for any excuse to primary every establishment senator who gives an inch to Clinton. We could see Benghazi-style investigation after investigation, with every vote aimed at making Clinton a one-term president and Congressional leaders searching for any and every chance to impeach. In this future, scraping together a few needed Republican votes could be a thing of the past, as the base looks for retribution from Republican senators who they feel betrayed Donald Trump and view any compromise as treasonous.

A Republican Senate could also continue its outrageous obstruction of both executive and judicial nominations, blocking highly-qualified people who want to serve the public from doing the work the government is meant to do. Hillary Clinton’s policy priorities--from reforming our campaign finance system, our immigration policies, our gun violence prevention laws, our criminal justice system -- could be stymied by Republicans more committed to obstruction than to doing the jobs they were elected to do.

Less than two weeks out from the election, these radically different scenarios are both entirely possible. The difference between night and day could come down to a single vote in the Senate. And both parties understand the stakes. Why else would a Republican super PAC connected to Senate Majority Leader Mitch McConnell be throwing an eye-popping $25 million into a handful of tight Senate races at the last minute?

Many voters this election are understandably consumed by what’s happening at the very top of the ticket. Preventing the election of a man whose contempt for immigrants, women, and people of color is only matched by his disrespect for our entire democratic system is a top priority, no doubt about it. But what happens on November 8 in competitive Senate races will determine how much the next president will be able to accomplish in their time in office. Electing the Republican senators who held their noses and pandered to Donald Trump wouldn’t just excuse their cowardly political calculation, it would mean a much steeper climb for any significant progress under a President Clinton.

Voters have a clear choice not only on the next president, but also on whether or not that president will face continued, or even increased, gridlock and obstruction. This election is more than just an exercise in getting over the 270 threshold for a victory. We have to trounce Donald Trump and all that he stands for, lest Trump and his followers claim for the next four years that the election was stolen. But that’s not enough. Of course, taking back both houses of Congress would bring back a working government--but we all must do all that we can do to at least take back the Senate.

The tale of the two Clinton presidencies, with or without the Senate, shows the starkest of contrast.