In an email to supporters, McConnell's campaign manager, Jesse Benton, touted his boss's Tuesday floor speech announcing his opposition and made a plea for donations at the end.

"Mitch's speech was one of the most well reasoned and thorough arguments that I have ever heard on the Senate floor. It's clear that he has dedicated himself to understanding the Syrian situation inside and out, and that he is fighting for Kentucky on the national, and international, stage," he wrote.

"Today was a ringing example of why we need to keep Mitch fighting for us in the United States Senate. Anything that you can contribute will go a long way towards our goal," Benton closes.

The email came just hours after McConnell declared on Tuesday morning that he'd be opposing military action in Syria because “being credible on Syria requires presenting a credible response, and having a credible strategy. And for all the reasons I’ve indicated, this proposal just doesn’t pass muster.”

The campaign of Kentucky Secretary of State Alison Lundergan Grimes (D), who is challenging McConnell, called the senator's fundraising appeal disgraceful.

"Senator McConnell's fundraising email is outrageous and shameful. It is politics at its worst. Senator McConnell is exploiting the tragedy in Syria for his own political gain," said Charly Norton, Lundergan Grimes' spokeswoman. 

"It took him weeks to tell Kentuckians where he stood, yet only seconds to fundraise off of this humanitarian crisis." 

McConnell's campaign hit back, charging that Lundergan Grimes was seeking to distract from her position on Syria, which spokeswoman Allison Moore said aligns her with Obama. 

"The lengths that Alison Lundergan Grimes is willing to go to distract voters from her support of President Obama's Syria plan is embarrassing. The reality is that she's been unmasked for her unwavering support for Obama administration policies and she's desperate to cover her tracks," Moore said.

Lundergan Grimes said previously she wanted to make sure there was a clear exit strategy before moving forward with strikes.

McConnell's comments opposing strikes on Syria came shortly after a compromise proposed by Russia began to emerge as a potential solution to the conflict, which has sharply divided both parties.

McConnell's opposition made him the only Republican leader to oppose military strikes. But it aligned him with the conservative wing of his party, and his conservative primary challenger, Matt Bevin.

-- This piece was updated at 11:47 a.m. to reflect comment from McConnell's campaign, and was updated again at 2:41 p.m.