Amid a bitter battle for one of the most contested Senate seats in the country, Sen. Mark Kirk, R. Ill., is taking aim at Democratic Rep. Tammy Duckworth for her refusal to say whether she will testify in a lawsuit over her alleged mistreatment of whistleblowers at the Department of Veterans Affairs.

The controversial case, which is based on workplace complaints filed by two VA employees who worked under Duckworth, is slated for trial in August.

Duckworth, herself an Iraq War veteran, served as director of the Illinois VA before receiving an appointment from President Obama to become assistant secretary of veterans affairs in 2009. The lawsuit was tossed out of federal court in 2008 after a judge concluded the complaints of the two VA whistleblowers were not protected by the First Amendment because they were lodged by government employees.

But the case is back for the second time in Illinois state court, where a Union County judge ruled last month that the trial could be held before Duckworth contests Kirk's vulnerable Senate seat in November.

Speaking to reporters Tuesday evening, Duckworth avoided questions about whether she planned to testify at the upcoming trial.

"I am looking forward to getting the truth out, you know, bottom line, Mark Kirk's comments on what's happening there is about as real as his phony claims for heroism and that he served in combat," she said before concluding her press conference.

Kirk came under fire during the 2010 Illinois Senate campaign for exaggerating aspects of his military career, a controversy he addressed by releasing personnel records from his time in the Navy Reserve before going on to win the race.

According to court filings, one of the VA whistleblowers involved in the case accused Duckworth of firing her in retaliation for raising concerns about conditions in a VA nursing home. Duckworth allegedly told the VA worker she had been "insubordinate" by filing a whistleblower complaint with the VA inspector general.

The VA whistleblower said Duckworth then "humiliated" her by announcing to the entire staff that the worker had just been fired and "in a loud voice" calling for security to escort the whistleblower off the premises.

The second VA worker involved in the case claimed Duckworth threatened to fire her shortly afterward, noting Duckworth told her she should "keep [her] mouth shut."

In a 2007 email to VA staffers that has been circulated by the Kirk campaign, Duckworth admitted she "screwed up in firing" the worker who complained to the inspector general because the whistleblower had to be placed on administrative leave before she could be terminated.

"I need documentation from you, in a clear, user-friendly format to justify my decision to fire her," Duckworth wrote to her VA colleagues.

Matt McGrath, spokesman for the Duckworth campaign, accused Kirk's team of twisting the details of the case in an effort to make their Democratic rival look bad.

"Tammy has complied at every step of this process, even as the civil case has stretched out over eight years and been dismissed in full or part three different times," McGrath told the Washington Examiner. "The Kirk campaign, meanwhile, has made it clear they have nothing more to offer Illinois families and are going all-in on their bogus version of this case — a version that is as phony as Mark Kirk's military record."

Duckworth did not attend a May 12 hearing for the case, during which a judge ordered the case to trial, because she was in Washington, D.C. attending a fundraiser with Sen. Harry Reid.

Because the state attorney general's office is handling Duckworth's defense, Kirk has pointed out that the case is continuing on the taxpayer's dime.

Illinois Republicans have seized on the VA case amid growing national anger over the lack of accountability at the VA.

Timothy Schneider, chairman of the state's Republican Party, said Wednesday Duckworth "owes Illinois voters an explanation."

"As a candidate for U.S. Senate, Duckworth owes it to Illinois voters to testify at her trial," Schneider said in a statement.

In addition to tying Duckworth to national VA failures, the Illinois GOP has highlighted her connections to former Democratic Gov. Rod Blagojevich, who was impeached and is presently serving jail time for corruption.

Blagojevich named Duckworth to her VA post. He was convicted on charges that included soliciting bribes in exchange for an appointment to Obama's vacant Senate seat.

A poll conducted by the Kirk campaign found 63 percent of voters thought Duckworth should testify at her trial, although the results broke down along party lines.

Kirk's Senate seat, which was once occupied by Obama, is considered one of the most vulnerable Republican seats in the country due to the Democratic tilt of Illinois.

Duckworth has attempted to capitalize on controversy surrounding the presumptive Republican presidential nominee by linking Kirk to some of Donald Trump's most unpopular statements.

Kirk walked back his support of Trump Tuesday following a backlash over comments the real estate mogul made regarding the judge who will rule on the Trump University case. In that lawsuit, former students of Trump's eponymous education program alleged they were promised results that instructors never delivered.

Shortly before she refused to answer questions about testifying in her VA trial Tuesday, Duckworth claimed "full credit" for "pushing Mark Kirk to back off his endorsement of Donald Trump."

In a poll conducted earlier this year, Trump trailed presumptive Democratic nominee Hillary Clinton by 25 points in Illinois.