Without California’s top two election system, Kevin de León would not be running against Dianne Feinstein for U.S. Senate right now.

That runs contrary to the conventional wisdom, which – like everything else about top two—is wrong.

That conventional wisdom is that the top two favors the incumbent Dianne Feinstein because, as the more politically moderate candidate, she can put together moderate Democratic voters, centrist independents, and Republicans into a broader, winning coalition. This wisdom tracks the promises of top two’s backers – and the claims of top two’s defenders and their many friends in the media – that the system favors moderates.

Put simply, it doesn’t. Indeed scholarship on top two systems in California and elsewhere – and, more recently, hard-won experience – show that top-two works against centrists. Instead, top two increases the advantage of the more ideological candidates of left and right.

Why? A couple reasons. First, because hard left and hard right voters are far more reliable voters than those of us in the center.

Second, because people vote more for the party than the candidate.

Think about Feinstein or any other Democratic centrist candidate in a race against a Democratic candidate to her left, with some weak or little known Republicans in the race.

In the first round of voting (which is really the general election but is called the primary), Feinstein can’t count on Republican votes, because Republican voters cast ballots for Republicans over Democrats, even those they’ve never heard of. She’ll need to win over centrists – who don’t vote as often – and then get as many Democrats on the left as she can.

In the runoff, presumably a two-person race with De Leon, will find that few Republicans will bother to vote at all. She’ll be running the same center-left race again.

We saw these dynamics play out in California in 2016, in the U.S. Senate race. The more left Democrat—Kamala Harris – was stronger in both rounds. The moderate, Loretta Sanchez, was well behind in the first round, and utterly failed to win significant Republican support in the second round. Republican voters stayed home. Reliable left voters tilted the electorate decisively in Harris’ way.

The candidates and political consultants know this. Which is why you see Feinstein running so hard to the left. She does not want to hold the political center and reach out to Republicans. To keep her seat, she needs to capture the Democratic base and win with many of the most liberal voters—in both rounds of the election.

And that’s a key point. The two candidates will be running against each other twice – in June and November. That advantages De León, who needs to build statewide name ID. He’ll also get two chances at her, and should be stronger in November for the June warm-up.

De León still faces an uphill battle against a respected and widely endorsed incumbent. But victory is possible in today’s California—because of top two.