The hotly contested race between Democrat Conor Lamb and Republican Keith Rothfus has achieved a milestone: Rothfus has aired the first attack ad in the 17th Congressional District. And he's apparently hoping that a mouse will roar.

“Who’s Conor Lamb protecting?” asks the 30-second TV spot, which has appeared on local airwaves in recent days. “Not seniors: Lamb supports a program that took billions from Medicare. Not the sick: Lamb wants to keep higher taxes on prescriptions and insurance. Not families: Lamb voted to protect criminals hiding in sanctuary cities.”

“Who is Conor Lamb protecting?” the spot then asks. “A mouse. Lamb voted to spend tax dollars to protect mice. Seriously.”

The Rothfus campaign backed up the ad with a statement asserting that Lamb “has already proven to be a reliable vote for liberals in Congress."

“Lamb has spent the last year trying to convince voters otherwise, even going so far as brandishing a high-powered rifle in an ad,” Mike Barley said an e-mailed statement. “But his efforts don’t pass the smell test.”

The statement notes that Lamb, like almost all other Democrats, voted against a measure that would have barred federal funding for the Preble’s meadow jumping field mouse, an endangered species native to Colorado and Wyoming. The mouse has been at the center of a number of conservation fights, with environmentalists using the designation to protect natural habitats over the opposition of developers and land owners.

To justify the sanctuary city claim, the campaign points to Lamb’s vote against the “Securing America’s Future Act of 2018,” a hard-line anti-immigration bill. The bill was defeated by opposition from 193 Democrats -- and also 41 moderate Republicans. Rothfus voted for the bill, one section of which would have stripped Homeland Security and Department of Justice funding from states or cities that barred local officers from assisting federal immigration authorities.

Some of those "sanctuary cities," including Philadelphia, limit their assistance on immigration cases, citing legal concerns and a desire to shore up police relations with immigrant communities. But Republicans have seized on the issue, and some high-profile cases in which immigrants in such communities have gone on to commit crimes.

As for the Medicare and health-cost claims, the campaign notes Lamb’s oft-stated support for President Barack Obama’s Affordable Care Act, better known as Obamacare. Republicans have long claimed that the ACA puts Medicare at risk, because the law anticipated reduced Medicare spending over a decade.

Such claims have not impressed fact-checkers, who note that the envisioned savings come from efficiencies required of health care providers, rather than patients themselves -- who gained new drug and treatment benefits. And health care experts have warned that previous Republican efforts to repeal the ACA would have their own damaging effects on Medicare.

The spot appears to be the first attack ad of the general election cycle. Rothfus has otherwise run upbeat ads that reintroduce him to voters with an account of his treatment for cancer, as well as a humorous spot in which, like commercials in earlier campaigns, his mother plays a prominent role.

But unlike those earlier spots, one of which lampooned President Barack Obama for golfing too much, the new ad is responding to a serious rival. Lamb gained national attention this past spring, when he pulled off a surprise win against state Rep. Rick Saccone in a special election to replace Tim Murphy in the old 18th Congressional District. Lamb and Rothfus were since drawn into the same Congressional District by a court-ordered redistricting -- and polling suggests Lamb holds a solid lead.

The new ad’s cartoonish rendering, which is not unusual for attack spots, may remind some viewers of the onslaught of TV ads Lamb faced. In that race, outside groups tied to national Repoublicans spent millions of dollars on Saccone.

But the new spot is also notable for what it doesn't say. Unlike the ads earlier this year, it makes no mention of Nancy Pelosi or a Republican tax-cut bill. Such attacks failed to head off Lamb in March, and national polling suggests that the tax cut in particular has gained little traction with voters.

Still, Lamb has touted that win -- and his defiance of those national ads -- in his own introductory spot ths fall.

The Lamb camp alluded to the earlier attacks when it fired back in a statement Thursday evening.

“Voters have been inundated with these cartoonish attack ads since January. Now apparently Keith Rothfus is going to make us all suffer through them again,” said Lamb campaign manager Abby Nassif Murphy.

Murphy’s statement noted that Rothfus had repeatedly voted in favor of repealing the ACA, adding that “protections for people with pre-existing conditions are part of that law.” She said Lamb would “work to improve the ACA and uphold its protections for pre-existing conditions."

On immigration, she stated that Lamb “knows it’s important for all levels of law enforcement to work together, and for elected officials to encourage cooperation and communication.”

Murphy's statement did not take a position on whether cities should be punished for failing to offer all the cooperation that federal agencies sought. But she did characterize the immigration measure as “an extreme partisan bill” that failed to make “smart border security investments” or to protect so-called immigrants who were brought to the United States at a young age and have limited connection with their parents’ home countries.

The statement cited those shortcomings as a reason “many Republicans voted against it" – and why it didn’t pass.

As for the Prebel’s meadow mouse? “We’re not going to fall into this trap," Murphy said.