Attorneys for Gov. Doug Ducey say he has the right to appoint Martha McSally, above, to fill the U.S. Senate seat once occupied by John McCain.

PHOENIX — Gov. Doug Ducey is asking a federal judge to throw out a lawsuit demanding that he call an election — and soon — to fill a U.S. Senate seat following the death of John McCain, rather than let Martha McSally keep the post until 2020.

In legal papers filed Friday, attorney Brett Johnson, who is leading Ducey’s legal team, acknowledged that vacancies in the U.S. House must be filled by a special election. But Johnson told U.S. District Judge Diane Humetewa that the U.S. Constitution allows the Legislature to let Ducey name a senator to serve until the next regular election.

And the fact that election won’t be until 27 months after McCain’s death last August, he said, does not change that.

Anyway, Johnson said, a special election solely to name a replacement would not just be expensive but also would give the edge to wealthier candidates.

In a lawsuit filed last year, attorney Michael Kielsky, chairman of the Arizona Libertarian Party, contends that the governor must call a special election as soon as practicable to fill the post, a period he said is no longer than six months. Kielsky, representing two registered Democrats, one Republican, one Libertarian and an independent, said there is no reason for an unelected person of the governor’s choosing to be able to serve through the end of 2020.

But Johnson said Ducey, who first appointed Jon Kyl and, later, McSally after Kyl quit, said Johnson is misreading the law.

There is no question but that Arizona law allows a governor to appoint a temporary replacement when a Senate vacancy occurs. That person has to be of the same political party as the senator who quit or died.

And the law does require that there be an election to determine who gets to finish out the balance of the term. In McCain’s case, his term ran through 2022.

Johnson, however, said if the next regular election is not within six months, then the appointee can serve until the regular election after that.

In this case, McCain died on Aug. 25. That was just three days before last year’s primary and 73 days before the general election. Based on that, Johnson said, Ducey had the power to name someone to serve until the 2020 election when the final two years of McCain’s term will again be up for grabs.

Kielsky, however, wants Humetewa to rule that voters should get a chance to name someone of their choice long before the 2020 election — a person who could be of any political party.

Johnson, in his new legal filing, said the “inconvenience and expense of a special election outweighs any advantage to be derived from having a more prompt vacancy election.”

He told the judge a special statewide election in 2016 dealing with school finance cost the state more than $6.4 million. And in this case, Johnson said, a special election would require both a primary and general election.

Johnson also claimed that a special election would give an edge to “special interest groups and candidates with considerable self-wealth or funding” because of the cost of having to finance an off-year campaign. By contrast, he argued, having the vote to fill the balance of the Senate term at a regularly scheduled election “creates a greater opportunity for a stronger pool of candidates to run.”

And Johnson said special elections have a lower turnout.

Johnson also brushed aside the complaint that the current practice is unfair because it means the person that the governor appoints has to be of the same political party as the person being replaced.

No date has been set for a hearing.