PHOENIX — Attorneys for the state and Republican legislative leaders are asking a federal judge to throw out a lawsuit by Democrats challenging the way candidates are listed on the ballot.

Attorney Mary O’Grady, representing Secretary of State Katie Hobbs, does not dispute that a 1979 Arizona law spells out that the party whose candidate got more votes in the last gubernatorial election in each county gets to list its candidates first. That means that in 2020 GOP candidates will be listed ahead of Democrats in 11 of the state’s 15 counties.

But in new legal filings, Ms. O’Grady told Judge Diane Humetewa that even if people tend to choose the first person on the ballot, that doesn’t make the system illegal.

“Arizona’s ballot order statute establishes logical, efficient, and manageable rules that determine the order in which candidates’ names appear on a general election ballot,” Ms. O’Grady wrote. And she argued that nothing in the law precludes those who have sued — Democrats and Democrat organizations — from voting for the candidates of their choice.

In their lawsuit, the challengers say the statute is illegally “diluting” some people’s votes, citing research which shows that, everything else being equal, people tend to vote for the first candidate on the list.

They said that can be important, citing what is expected to be a tight race for the U.S. Senate.

Republican Martha McSally, appointed to the seat that used to belong to John McCain, faces a stiff challenge from Democrat Mark Kelly. If the law remains in place, Ms. McSally will be in the No. 1 position in most counties, including Maricopa where most voters live.

But attorney Kory Langhofer, representing Senate President Karen Fann and House Speaker Rusty Bowers, argued that even if there is some such edge for the first position on the ballot — what he said has been dubbed the “donkey vote” — that does not make it an unconstitutional government-imposed burden. Anyway, he told Ms. Humetewa, it’s not like ballot order is the only thing that might make people decide how to vote.

“Even assuming that the ‘donkey vote’ exists, and even if it were possible to quantify its precise impact on election outcomes, ballot order is merely one of many cognitive shortcuts that voters employ in their electoral decision-making,” Mr. Langhofer wrote. He said there are other studies which show the impact of party label, incumbency, gender, name familiarity and even “religious-ethnic cues apparent from candidate surnames” that may influence voters’ decisions.

Ms. O’Grady, in her own arguments, told Ms. Humetewa that there are even simpler reasons for the judge to throw out the case.

First, she said, the individuals that sued lack legal standing, as they have suffered no particular harm — other than being unhappy about election results. And she said that does not change even if some voters do lean toward selecting the first candidate listed.

“The lack of an entirely rational electorate is not an injury-in-fact’ necessary to invoke (constitutional) standing,” Ms. O’Grady wrote.

She similarly argued that the committees who sued, including the Democratic National Committee, the Democratic Senatorial Campaign Committee, and Priorities USA, a political action committee that backs Democrats, also have not identified any members who are actually harmed. Instead, Ms. O’Grady said, the groups are alleging “nothing more than a statistical probability that some of its members might be injured,” an allegation the attorney said is not enough to sue.

But that does not mean such a lawsuit is legally impossible.

“Candidates themselves may have standing to bring the equal protection claim alleged,” Ms. O’Grady wrote.

A hearing is set for March.

Much of the focus is on Maricopa County, where unless the law is enjoined, nearly two-thirds of the state population will get ballots with Republicans in top position in every partisan race.

According to the lawsuit, Maricopa voters have favored Republican gubernatorial hopefuls in all but two elections in the nearly 40 years that the ballot order statute has been in place. The only exceptions have been in 1982 when they supported Democrat Bruce Babbitt over Republican Leo Corbet, and in 2006 when Janet Napolitano, seeking a second term, outpolled Republican Len Munsil.