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As speculation on whom the presidential nominees will select as their running mates gets louder, almost inevitably eyes are turning to Massachusetts senator Elizabeth Warren. Joe Biden apparently wanted her to be his vice presidential candidate if he ran for president this year. She’s gleefully turning herself into a thorn in Donald Trump’s side. And as Sam Stein and Ryan Grim report, people within Hillary Clinton’s campaign are pushing her to select Warren as her running mate.

My dear liberal friends, I can feel your excitement already. But while Warren will be a great anti-Trump surrogate for Clinton — maybe the best Clinton will have — she’s not going to be on the ticket. Sorry to deliver the bad news.

There are a few reasons for this. The first is that Clinton and Warren aren’t close or even particularly friendly, and personal rapport is a key part of an effective working relationship between the president and vice president, as Clinton surely understands. Warren would come to the office with her own agenda on economic affairs — an agenda more aggressively liberal than Clinton’s, particularly when it comes to how the government should deal with Wall Street. Warren would also bring her own constituency, which could make her an unwanted headache for Clinton, who like all presidents would want a vice president who has no goal other than advancing the president’s goals.

Second, picking Warren would make for a historic all-female ticket, and that could be a risk. To be clear, it’s ludicrous that there should be something troubling to anyone about having two women running together. After all, we’ve had over a hundred all-male tickets in our history, and only two with one man and one woman. But there could well be some number of voters — how many is difficult to tell — who would vote for Clinton with a male running mate, but would find Clinton with a female running mate just too much to handle. It’s sexist, but Clinton is going to need the votes of people who have some sexism somewhere in their hearts, just like Barack Obama needed the votes of people with some racism somewhere in their hearts.

And Hillary Clinton is nothing if not a risk-averse politician. She’s been blessed with Donald Trump as an opponent, and she isn’t going to take any big chances between now and November that might complicate things.

Third, and probably most important, right now the governor of Massachusetts is a Republican, Charlie Baker. That means that if Warren stepped down to become vice president, Baker would appoint a temporary successor for her Senate seat. In other years this might have been a relatively minor consideration, but in 2016 it’s absolutely central to the fate of Clinton’s presidency.

With Hillary Clinton leading in the Democratic presidential primary, The Washington Post's Chris Cillizza says these are the five people the former first lady might pick as her running mate if she makes it to the general election. (Sarah Parnass/The Washington Post)

Right now Republicans have a 54-46 advantage in the Senate, but they’re defending many more seats up for reelection. Seats in Democratic-leaning states like Illinois, Wisconsin, and New Hampshire may well turn to the Democrats, but it’s likely to be very close. It’s entirely possible that we could have a Senate that’s 51-49 for the Democrats, or even 50-50. One vote could make the difference between Clinton getting her nominees confirmed and having some chance at legislation passing (depending on what happens with the filibuster and the House), or finding herself utterly paralyzed by Congress. Giving up a seat for the sake of a compelling running mate is an enormous risk, one Clinton would be foolish to take. Which, by the way, also rules out a number of other potential vice presidential candidates, including Sherrod Brown of Ohio and Cory Booker of New Jersey.

And though Warren won’t rule out accepting a spot on the ticket if it’s offered, there are good reasons why she would view the vice presidency as a step down. It won’t be a springboard to a presidential campaign, since Warren turns 67 next month, and if Clinton were to win and then run for reelection in 2020, the next chance Warren would have would be in 2024, when she’ll be 75 and probably too old for a bid. Warren has built her career on policy entrepreneurship (the Consumer Financial Protection Bureau was her idea, and she has advocated for initiatives like postal banking), but as vice president she’d have to just sell whatever President Clinton wanted to do. If she stays in the Senate, she can keep using her office as a platform to advocate on the issues that are important to her, and she can probably keep her seat for the rest of her life if she wants to.

The good news for Warren’s fans is that it looks like she’ll still have an important role to play in the general election. She has turned her Twitter feed into an unceasing string of criticisms of Donald Trump, and not too surprisingly, it has gotten under his skin (Trump obviously finds it deeply unsettling when a woman stands up to him). He has countered by dubbing her “Goofy Elizabeth Warren,” which is not exactly the most stinging moniker he has come up with.

Warren’s popularity on the left means she could play a key role in convincing Bernie Sanders’ supporters to get behind Clinton, and the plainspoken charisma that made her a star in the first place will also make her a sought-after surrogate for Clinton in the media. All of which means that once the election is over, she’ll return to the Senate in an even stronger position than she was in before. Don’t be surprised if Warren — to an even greater degree than Sanders — becomes the clear leader of the party’s liberal base as it grapples with a Democratic president with centrist impulses. That could make her even more important than if she had been vice president.