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WASHINGTON - Senate Republican Leader Mitch McConnell is seizing on the scandal at the Internal Revenue Service in a new campaign advertisement, using vintage video footage of Richard Nixon to amplify his criticism of President Obama and his administration.

No opponent has yet emerged to challenge McConnell in Kentucky, so he is biding his time by sharply condemning the Obama administration in the wake of the IRS acknowledging that conservative groups had been unfairly targeted.

It is the clearest sign yet the IRS controversy is likely to play a central role in the midterm elections next year.

The new online ad for McConnell, obtained by ABC News, seeks to draw comparisons between Nixon and Obama. It shows a famous clip from an interview with David Frost, where Nixon declares: "When the president does it, that means it's not illegal."

It is the first political ad of the year to show IRS officials on the hot seat at recent Congressional hearings. One employee is shown taking the Fifth Amendment and declining to testify, while two others repeatedly say they were unaware of the targeting underway by the IRS.

The Web video also stitches together speeches that McConnell has been delivering for more than a year. It raises questions about government intimidation and the IRS treatment of Tea Party groups and others applying for tax-exempt status.

"I think that the leader of the free world and his advisers have better things to do than to dig through other people's tax returns," McConnell says.

While McConnell is one of the top targets of the 2014 election cycle, Democrats have struggled to field a challenger, and talk of a Republican primary race has not materialized, in part because McConnell is building a presidential-size campaign in hopes of being re-elected to a sixth term in the Senate.

The president moved quickly to respond to the IRS scandal after it became public, but the White House has struggled to explain a consistent sequence of events about which administration officials were aware of the investigation inside the IRS.

Jesse Benton, the campaign manager for McConnell, said the IRS controversy speaks to anxieties and concerns voters have about the government.

"He's going to keep pushing on it," Benton said in an interview. "There are a great majority of Americans that would agree, regardless of political party, that we need to hold ourselves to a higher standard. Americans of good conscience across the ideological spectrum are going to band together and say this is enough."

The online ad called "Demand Answers" was produced by Lucas Baiano, a videographer who is known for making iconic video images for Republican candidates. It is the third ad he has made for McConnell.