Senate Minority Leader Mitch McConnell (R-Ky.) on Tuesday broke his official silence in the Bluegrass State’s contested GOP Senate primary by formally endorsing Secretary of State Trey Grayson.

McConnell, who has been working behind the scenes on Grayson’s behalf, is also starring in a TV ad in which he tells his Kentucky constituents, “I know Trey Grayson, and trust him.”

“I rarely endorse in primaries, but these are critical times,” McConnell says in the ad. “We need Trey’s conservative leadership to help turn back the Obama agenda.”

While most public polls have shown Grayson trailing eye surgeon Rand Paul by wide margins in the race for the GOP nomination, the Grayson campaign released an internal poll that backs up the position that the nomination can go either way. Grayson and Paul were tied with 40 percent each, with 20 percent undecided.

McConnell’s endorsement comes one day after Rep. Hal Rogers (R-Ky.) endorsed Grayson. However, the bigger news on Monday was that Grayson lost the endorsement of Dr. James Dobson, an influential voice among social conservatives who defected to support Paul’s campaign.

Paul and Grayson are seeking the seat currently held by retiring Sen. Jim Bunning (R). Bunning is supporting Paul, who has courted the support of the tea party movement in his campaign.

The eventual GOP nominee will face either Lt. Gov. Daniel Mongiardo or Attorney General Jack Conway, who are squaring off in the Democratic primary.