Republican presidential candidate Donald Trump points to the crowd while speaking at a rally Tuesday in Cedar Falls, Iowa. (Jae C. Hong/AP)

A federal judge on Thursday rejected an effort by Donald Trump supporters to block the use of a party loyalty pledge in Virginia’s Republican presidential primary on March 1.

In her decision, U.S. District Judge M. Hannah Lauck ruled that there wasn’t enough evidence to show that voters would suffer “irreparable harm” by signing a party affiliation statement before receiving a ballot on Super Tuesday, as Trump’s supporters argued.

The testimony “does not support the extraordinary remedy of a preliminary injunction” against including the requirement on instructions for ballots issued on election day or absentee ballots mailed to registered voters outside the state, Lauck ruled.

The lawsuit, filed this month in the Eastern District of Virginia on behalf of three pastors who support Trump, stems from the state Republican Party’s decision in September to require voters to sign a “statement of intent” before taking part in the primary.

The pledge, already on ballot instructions printed across the state, reads: “My signature below indicates I am a Republican.”

That idea, which has been proposed several times in recent years, has caused controversy in Virginia, one of about 14 states that hold “open primary” elections in which voters do not register by party.

Trump elevated the issue to national significance when he called the pledge a “suicidal mistake” that would turn away voters who are disenchanted with traditional party politics — many of whom support his presidential bid.

“It will turn away new Republican voters,” Corey A. Stewart, who heads Trump’s political operation in Virginia, said Thursday in reaction to the ruling. “But the establishment in Virginia doesn’t care. They would rather keep it small and keep it all, in terms of control.”

The plaintiffs in the case filed a request for a preliminary injunction pending their appeal in the U.S. District Court of Appeals and were denied that request.

In Virginia, the open primary system stems from desires for political control, said Mark J. Rozell, acting dean and professor of public policy at George Mason University’s School of Policy, Government, and International Affairs.

The system has been in effect for decades, going at least as far back as the days when Harry F. Byrd dominated state politics as the leader of the state Democratic Party during much of the first half of the 20th century. Byrd served as a state senator, Virginia governor and U.S. senator before retiring in 1965 after 50 years in politics.

Back then, Byrd’s political machine usually ensured a Democratic victory, so it didn’t matter much whether Republicans also voted in party primaries, Rozell said.

“Given the one-party dominance in the state for many years, conservative Republicans had little choice other than to vote in Democratic primaries if they wanted to influence election outcomes,” he said. “Back then, nomination by the party guaranteed election.”

Today, Republican Party officials argue that there is too much potential for Democrats and independents to interfere with an already contentious presidential primary election that has 13 Republican candidates — making a loyalty pledge necessary.

In the lawsuit, they cited a Virginia election law that allows political parties to decide how to conduct primary elections, even if the state is coordinating the process with taxpayer dollars.

“Political parties have a right to determine how they nominate the candidates who represent them,” John Findlay, the state Republican Party’s executive director, said in a statement Thursday. “The Republican Party of Virginia has a duty to defend its First Amendment right to free association, and we are very pleased that the court has denied the preliminary injunction, as we expected.”

The lawsuit’s plaintiffs — African American pastors Stephen A. Parson, Bruce L. Waller Sr. and Leon Benjamin — argued that the pledge will discourage minority voters and those who are poor from casting ballots. They also said that confusion about the pledge will lead to long lines at the polls, imposing a “burden of fear and backlash” that amounts to a literacy test for uneducated voters.

“This is not something we’ve engaged in or embarked on lightly,” Chuck Smith, who represents the pastors, said of the legal battle. “This issue is very important to Republicans, very important to the citizens of Virginia and, obviously, very important to the three plaintiffs.”

Carl Tobias, a professor at the University of Richmond’s School of Law, said there may be maneuvering room for Trump supporters to continue the fight in the U.S. Court of Appeals for the 4th Circuit.

In her ruling, Lauck expressed concern that absentee ballots being mailed out this week have instructions dealing with the loyalty oath that are different from what is printed for in-person ballots.

Absentee ballots carry language saying that a signed statement of intent will ensure that the ballot can be counted, but in-person ballots say a voter “refusing to sign the statement form cannot vote in this Republican Party nominating process,” Lauck noted.

The small difference could lead to potential voter confusion on March 1, Lauck wrote, calling it a matter “of significant concern.”

“I think what she is concerned about is that the voters have what they need in order to vote properly and understand what they’re doing,” Tobias said. “It could well be appealed by plaintiffs to the 4th Circuit.”

In other words, he said, “This could continue.”