ADVERTISEMENT
Rubio's help on the trail should boost McConnell's credibility with Tea Party voters in Kentucky, a group that's long been wary of McConnell's record in the Senate. Some Tea Party groups have been actively pursuing a primary challenger to McConnell, but no possible contenders have yet jumped into the race.

"Mitch McConnellAddison (Mitch) Mitchell McConnellSenate passes 0B defense bill Overnight Health Care: New GOP ObamaCare repeal bill gains momentum Overnight Finance: CBO to release limited analysis of ObamaCare repeal bill | DOJ investigates Equifax stock sales | House weighs tougher rules for banks dealing with North Korea MORE's quiet, principled leadership is key to everything we accomplish on Capitol Hill," Rubio said during the event, according to CNN.

"The way he fought ObamaCare, tooth and nail, and forced the Democrats to use extraordinary measures to pass it was a critical catalyst in electing my entire class of Senate conservatives in 2010. Without Mitch, I don't know that we'd have Senator Rubio, Senator Johnson, Senator Paul or Senator Lee."

Sens. Ron JohnsonRonald (Ron) Harold JohnsonSenate Dems hold floor talk-a-thon against latest ObamaCare repeal bill Sen. Cassidy plans to bring down Medicaid Senate committee schedules hearing on health care block grants MORE (R-Okla.), Rand PaulRandal (Rand) Howard PaulSenate Dems hold floor talk-a-thon against latest ObamaCare repeal bill Overnight Defense: Senate passes 0B defense bill | 3,000 US troops heading to Afghanistan | Two more Navy officials fired over ship collisions Lawmakers grapple with warrantless wiretapping program MORE (R-Ky.) and Mike LeeMichael (Mike) Shumway LeeOvernight Defense: Senate passes 0B defense bill | 3,000 US troops heading to Afghanistan | Two more Navy officials fired over ship collisions Senate passes 0B defense bill Overnight Finance: CBO to release limited analysis of ObamaCare repeal bill | DOJ investigates Equifax stock sales | House weighs tougher rules for banks dealing with North Korea MORE (R-Utah) all have Tea Party support, and affiliating himself with all three will likely help McConnell appeal to those skeptical voters on the right.

McConnell is likely to face a strong challenge from Democrats as well, who believe he is one of the nation's most vulnerable incumbents in 2014. Two Democratic contenders, actress Ashley Judd and Kentucky Secretary of State Alison Lundergan Grimes, have emerged as possible challengers.