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Sometimes the answer to a question is another question.

Q: How many people are going to vote in Tuesday’s Democratic and Republican primaries in Texas?

A: Which race?

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The presidential races at the tops of the two parties’ ballots have drawn the most attention, particularly the Republican contest. Those will attract voters, but it’s normal for many people to vote in the top race and leave.

In the Republican primary four years ago, one-third of the people who voted in the top race didn’t vote in the last statewide race on the ballot. Fewer people voted in the Democratic primary that year and the falloff was lower, but it was still significant, dropping 26.8 percent from the top statewide race to the bottom one.

More people voted early this year than in 2012 — the last presidential election year. Voters like competitive races, and it shows in the turnout numbers. Years with real contests for president, like the 2008 Democratic primary in Texas, see higher turnouts than years that don’t, like 2012.

And those ballots can see bigger differences in the number of voters who stick around after the top race. For the Democrats in 2008, the drop was 40.2 percent. The Republicans lost 31.4 percent of their primary voters from the top statewide race to the bottom one that year.

Candidates like Ted Cruz and Hillary Clinton don’t have to worry about this — their races are the first thing people see — but the candidates below them on the ballot pay attention.

The drop-off in voting in a primary can protect those downballot candidates from ideological stampedes at the top. The Trump-Cruz-Rubio wrangle in the top Republican race and the Sanders-Clinton rumble on the Democratic side don’t mean as much by the time voters reach legislative races.

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For one thing, there are no party labels to help guide voters through the field of candidates; it’s impossible to tell from what’s on the ballot which presidential hopeful is most in line with a particular candidate for Senate. Unless voters know something specific, they can’t tell whether their congressional favorites would be simpatico with their presidential favorites.

The drop-offs might provide some hope for judicial candidates and others not well-known to most voters. A lot of low-information voters are among those who come for the presidential race and then leave the voting booth; they won’t be around to make choices based on who has the coolest names.

It will be a different matter in November. Candidates on the general election ballot will have party labels next to their names. How voters feel about the people at the top of the ballot can make all the difference in who else they support — particularly if they are the types of Texans who pull the straight-ticket lever for their party instead of working their way through the list.

If you like the Republicans or dislike the Democrats, you pull that lever, and vice-versa. A particularly unattractive candidate at the top of the ballot can sour things for everybody else, just as a superstar at the top offers a coattail effect to those below.

Candidates in the primaries worry about unknowns, like whether the noisy Republican competition will pull new people to the polls who have rarely been there before. How do you poll them? Will they stick around for judicial and legislative races or vote for president and leave? And do they vote the same way as the Republicans who always vote, or should the campaigns fret over a wild-card effect, especially with disruptive candidates like Donald Trump and Bernie Sanders among the choices?

According to the Texas secretary of state, early turnout in the 15 biggest counties rose 102 percent in the Democratic primary and 92 percent in the bigger Republican primary. If early voting is a reliable indicator, turnout will be high this year in both parties.

So will the number of Texans who only vote for in their party’s race for president.