Americans for Prosperity, a conservative outside group backed by the Koch brothers, is launching a $1.8 million advertising campaign hitting Democratic Senate candidates in Iowa and Michigan on ObamaCare.

The group is also thanking Republican Rep. Steve DainesSteven (Steve) David DainesBooker signs on to Sanders's 'Medicare-for-all' bill Senate approves Trump's debt deal with Democrats Centrist Dem: Maybe we should look at single-payer health care MORE, running for Senate in Montana, for his opposition to the law.

The attack ads hit Democratic Rep. Gary PetersGary Charles PetersOvernight Regulation: House moves to block methane rule | Senators wrestle with allowing driverless trucks | EPA delays toxic waste rule Overnight Tech: Senate looks at self-driving trucks | Facebook to keep ads off fake news | House panel calls Equifax CEO to testify Senators wrestle with including trucks in driverless car bill MORE in Michigan and Bruce BraleyBruce BraleyOPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer MORE in Iowa, both their party’s likely nominees for open Senate seats in each state, for President Obama’s erroneous claim that Americans could keep their health insurance under ObamaCare.

“They told us the lie of the year,” a narrator says in the ad.

It goes on to include a clip of Peters repeating the claim on the House floor, and negative news from the law’s rollout.

“The truth is, 225,000 Michiganders have had their insurance canceled, families are losing their doctors and healthcare costs are skyrocketing. Call Congressman Peters and tell him ObamaCare isn’t working, it’s hurting Michigan families,” the ad closes.

The attack ads will be boosted by online and radio buys.

Democrats accused the Kochs of attempting to "buy themselves" a Senate.

“The Koch brothers are worth over $100 billion, so it’s no surprise they are spending a fraction of their fortune to buy themselves a U.S. Senate that works for them and against the middle class," said Democratic Senatorial Campaign Committee spokesman Justin Barasky.

He hit back against Michigan Republican Senate candidate Terri Lynn Land in particular, charging she "hasn’t done a single public event since becoming a candidate," and added that "the GOP field in Iowa is an absolute mess, so it’s no surprise that the Koch brothers are spending millions on desperate and false attack ads to prop up their lackluster candidates.”

They are the group’s latest offensive effort focused on the law, which Republicans believe will benefit them at the ballot box in November, as polling has shown Americans are still opposed to the law and that the rocky rollout hurt Democrats' standing nationally.

By its own count, Americans for Prosperity has spent about $20 million since August on advertising knocking Democrats and defending Republicans, largely focused on the healthcare law. Most recently, the group hit Arizona Democratic Reps. Ron Barber and Ann Kirkpatrick, two of the party’s most vulnerable House incumbents.

— This piece was updated to reflect comment from the DSCC.

Watch the ad: