Former United Nations Ambassador John Bolton is making his first two Senate endorsements of the cycle for Sen. Mitch McConnellAddison (Mitch) Mitchell McConnellSenate tees up Yemen vote for Tuesday Senate confirms Trump's border chief House leaves out ObamaCare fix from must-pass funding bill MORE (R-Ky.) and Rep. Tom CottonThomas (Tom) Bryant CottonRussian spy poisoning brings world powers closer to day of reckoning GOP senators see Tillerson ouster as the new normal Cotton: Russia will 'lie and deny' about British spy poisoning MORE (R-Ark.), who are running in two races that will be critical to control of the Senate this fall.

“After over seven years of Harry Reid’s failed leadership in Washington, America needs change. Having worked with Mitch McConnell, I know he is the Senate Majority Leader we need to lead Congress in the right direction,” Bolton said in a statement shared first with The Hill. 

“With a Senate victory in Arkansas from Congressman Tom Cotton, a GOP rising star and veteran who served in both Iraq and Afghanistan, I am confident the Republican Party will win back control of the Senate and turn back the clock on six years of botched Obama policies at home and abroad,” he added.

Bolton's political action committee will max out to both candidates, and is meeting with McConnell on Tuesday to make the endorsement in person and, an aide said, to discuss the need to strengthen American national security.

McConnell is a top target of Democrats; they’re running Kentucky Secretary of State Alison Lundergan Grimes, considered a strong contender, against him. Most recent polling of the race has shown them statistically tied, making this the toughest reelection fight of McConnell’s career.

Cotton was a top Republican recruit to take on Sen. Mark Pryor (D-Ark.), one of Democrats’ most vulnerable incumbents. That race is also tight, with the most recent survey, conducted by a GOP pollster at the end of May, giving Cotton a 5-point lead.

Republicans need to pick up six seats to take back the Senate, and Arkansas is a core target for the party, while Democrats see Kentucky as a rare opportunity for offense.

McConnell and Cotton are the third and fourth candidates Bolton has endorsed this cycle, after backing retired Air Force Col. Martha McSally, in a rematch with vulnerable Democratic Rep. Ron Barber (Ariz.), and Barbara Comstock, the Republican nominee for retiring Rep. Frank Wolf’s (R-Va.) seat.

Bolton is supporting candidates he believes support strong national defense. He also has a super-PAC, and through both groups he plans to make national security and foreign policy top issues this cycle.

The former foreign policy adviser to GOP presidential nominee Mitt Romney is looking at a potential presidential bid of his own and has become more active in electoral politics this cycle as part of an effort to raise his profile as he considers a run.