According to a 1999 New York Times report, McConnell, then chairman of the National Republican Senatorial Committee, issued an "urgent" fundraising plea for the committee that declared donations were needed to avert a potential nuclear attack by North Korea.

"Dear Fellow American: My colleagues in the United States Senate must have your immediate help to protect our country from a potentially devastating nuclear attack," the four-page letter read.

The letter came as North Korea prepared to conduct a test of a missile capable of reaching Hawaii or Alaska, a prospect that prompted the United States, Japan and South Korea to threaten to cut off aid to the nation.

McConnell wrote that a "generous emergency gift of $25 or more" could help Republicans in the Senate "do what President Clinton will not: preserve, protect and defend the United States of America."

A form gave donors the option to give anywhere from $25 to $1,000.

At the time the letter was sent, one campaign finance reform advocate told The New York Times that the letter's "fear-mongering techniques just takes my breath away."

The McConnell campaign did not respond to a request for comment on the North Korean fundraising letter.

Despite receiving criticism for the fundraising letter in 1999, McConnell again raised funds from his engagement in national security issues this week, this time on Syria.

In a fundraising pitch issued Tuesday, McConnell campaign manager Jesse Benton touted McConnell's Tuesday floor speech, in which he explained his opposition to Syrian strikes. The email includes 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 campaign of McConnell's Democratic Senate, Kentucky Secretary of State Alison Lundergan Grimes, called the fundraising pitch "shameful."

"Sen. McConnell's fundraising email is outrageous and shameful. It is politics at its worst. Sen. McConnell is exploiting the tragedy in Syria for his own political gain. It took him weeks to tell Kentuckians where he stood, yet only seconds to fundraise off of this humanitarian crisis," said Charly Norton, Lundergan Grimes's spokeswoman.

But McConnell's campaign in return accused Lundergan Grimes of "distracting" voters from her support for Syrian attacks. Grimes had previously said she wanted to see an exit strategy before any attacks went forward, a position somewhat more favorable towards military action than Rep. John YarmuthJohn Allen YarmuthRed state Dem: Trump has 'committed impeachable offenses' Congress reeling from sexual harassment deluge The nearly 60 Dems who voted for impeachment MORE (D-Ky.), who opposes attacks, had expressed.

It's not unusual for candidates to raise funds off of national security issues; House Minority Leader Nancy Pelosi (D-Calif.), in 2003 lent her name to a Democratic Congressional Campaign Committee fundraising email that asked for contributions to "get the 'war on terrorism' back on track by refocusing our efforts on the terrorists who started it," shortly after former Iraqi leader Saddam Hussein had been captured.

And then-Sen. John KerryJohn Forbes KerryFeehery: Oprah Dem presidential bid unlikely Dem hopefuls flock to Iowa Change in Iran will only come from its people — not the United States MORE's (D) presidential campaign issued a fundraising plea in 2004 that called for former Defense Secretary Donald Rumsfeld's resignation, following the emergence of details surrounding prisoner abuse at the Abu Ghraib prison in Iraq.

National Republican Senatorial Committee spokeswoman Brook Hougesen pointed out that Democrats, too, had issued similar pitches, and suggested criticism of McConnell's fundraising efforts was hypocritical.

"Apparently Democrats have no problem fundraising with troops on the ground fighting a war if a Republican is in the White House, but take issue with candidates who dare to point out how badly the Obama Administration has bungled their handling of the Syria crisis.  We look forward to Democratic critiques of Barack ObamaBarack Hussein ObamaMcCarthy: ‘No deadline on DACA’ Democrats will need to explain if they shut government down over illegal immigration Trump’s first year in office was the year of the woman MORE, John Kerry, Barbara BoxerBarbara Levy BoxerDems face hard choice for State of the Union response Billionaire Steyer to push for Dem House push Billionaire Steyer announces million for Dem House push MORE, and countless other liberals who set a precedent that they now claim to find so abhorrent," she said.

--This piece was updated at 1:45 p.m. to include comment from the NRSC.