The newest ad from Senate Minority Leader Mitch McConnell's campaign illustrates why his most valuable surrogate is his wife, former labor secretary Elaine Chao.

In it, Chao responds to a recent commercial from McConnell's opponent, Secretary of State Alison Lundergan Grimes (D). She offers a serious, direct-to-camera rebuttal to Grimes's argument — a central one in the Democrat's campaign — that McConnell (R-Ky.) has cast votes that have hurt women.

"Have you ever noticed how some liberals feel entitled to speak on behalf of all women — as if every woman agrees with Barack Obama," Chao says. "Alison Lundergan Grimes's gender-based attacks are desperate and false."

Here's Grimes's ad from last week in which she and a local woman criticize McConnell for voting against reauthorizing the Violence Against Women Act last year and the Lilly Ledbetter Fair Pay Act of 2009.

"I approve this message because, senator, you must be forgetting that over half the voters in Kentucky are women like Ilene," Grimes says in her commercial.

The ad with Chao says McConnell co-sponsored the original Violence Against Women Act and rejects the notion that he has failed to take women's interests into consideration with his votes.

There's nothing particularly remarkable about the messages in both ads. You'd find the same attacks and counterattacks in many other campaigns.

But in politics, the messengers are often as — if not more — important as the messages. In this case, Chao is as effective a messenger as McConnell could hope to have in his corner.

Grimes is running hard against McConnell on women's issues. Her argument is essentially this: McConnell is out of touch with Kentucky women. Just look at his rhetoric and his record.

Her argument — to women from a woman — holds the potential to spur Democratic and centrist women to come out to the polls and vote for her in the fall in what's shaping up as a very close race. That has placed a burden on McConnell to come up with an effective counterargument.

He's turning to Chao to make that argument — to women from a woman, just like Grimes. Not many male politicians have a spouse or significant other who is willing and able to play that role — let alone one as well known as Chao. (For more on Chao and her role in her husband's campaign, read Jason Horowitz's excellent NYT piece from May.)

Grimes is going to keep hitting McConnell on women's issues. We know that. We also know how McConnell is going to respond to most of those hits.

Sean Sullivan has covered national politics for The Washington Post since 2012.