Retired Marine Gen. John Allen says presumptive Democratic nominee Hillary Clinton is the right person to be the next commander in chief.

Allen, who led troops in Iraq and Afghanistan and served as the U.S. envoy to coordinate the international fight against the Islamic State group, said on Monday that Clinton has the patience and understanding to make smart decisions about using military power

"This has been a very personal decision for me," Allen said in Clinton campaign news release. "I have stayed out of the political arena my entire adult life, but given the complexities of issues facing our country today and its longtime allies, I felt compelled to speak up and be heard.

"I have no doubt that she is the leader we need at this time to keep our country safe, and I trust her with that most sacred responsibility of Commander-in-Chief."

Allen could not be reached for comment. Clinton thanked the retired general for his endorsement during her speech Monday at the Veterans of Foreign Wars convention in Charlotte, North Carolina.

"His confidence in me — and that of the other esteemed military leaders who support my campaign — means a great deal to me," Clinton said. "But it also imposes a high responsibility on me as well."

Bill Schneider, an expert on political campaigns, said that Allen's move could reassure some voters who are still on the fence about whether Clinton can be trusted as commander in chief.

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"That's very important because she would be the first female commander in chief in history," said Schneider, who is currently a visiting professor of communications at the University of California, Los Angeles. "It's an important statement because it shows that military people can work with her."

110718-N-TT977-138 U.S. Marine Corps Lt. Gen. John R. Allen, U.S. Army Gen. David H. Petraeus, commander, International Security Assistance Force and Chairman of the Joint Chiefs of Staff Adm. Mike Mullen arrive at the promotion ceremony for Allen at ISAF headquarters in Kabul, Afghanistan on July 18, 2011. (DoD photo by Mass Communication Specialist 1st Class Chad J. McNeeley/Released)

Marine Gen. John R. Allen, Army Gen. David Petraeus and Chairman of the Joint Chiefs of Staff Adm. Mike Mullen at Allen's promotion ceremony in Kabul, Afghanistan on July 18, 2011.

Photo Credit: MC1 Chad J. McNeeley, Office of the Chairman of the Jo

As a deputy commander in Iraq's Anbar province from 2006 to 2008, Allen realized that the key to defeating al-Qaida in Iraq was empowering the Sunni sheiks and tribes whom the coalition had tried to remove from Iraqi politics immediately after the fall of Saddam Hussein.

He helped form an alliance between U.S. and Sunni tribes known as the "Awakening" movement, which turned the tide against al-Qaida until U.S. troops left the country.

From 2011 to 2013, Allen served as the top commander of all U.S. and NATO troops in Afghanistan. Afterward, he was nominated to be the head of U.S. European Command but he opted to retire instead, saying he needed to care for his wife Kathy, who was in poor health.

Even though he has endorsed Clinton, Allen has not always seen eye-to-eye with President Obama, who is also a Democrat. Allen has consistently urged Obama to curtail the drawdown of U.S. troops in Afghanistan, telling Marine Corps Times in September 2014 that the withdrawal plan at the time could cause the Afghan government to collapse.

In June, Allen was one of 13 former military and civilian officials who wrote a letter to President Obama urging him to keep 10,000 U.S. troops in Afghanistan for the remainder of his time in office. Obama ultimately decided in July to keep 8,400 U.S. troops in the country until January.

In September 2015, Allen abruptly resigned from his position leading international efforts against ISIS amid media reports that he disagreed with White House and Defense officials about the best strategy to defeat the terrorist group.

Attempts to reach Allen for comment on Monday were unsuccessful.

As a general officer who is widely respected within the military community, Allen’s endorsement is significant to the Clinton campaign, said Mark Cancian, with the Center for Strategic and International Studies think tank in Washington .

"It protects Clinton against arguments that she may have been anti-military, at least at times in her past," said Cancian, senior adviser with the international security program at CSIS. "Certainly back in the '90s, when Bill Clinton was president, that was a huge issue."

Cancian, a retired Marine colonel who served with Allen in Iraq, has some concerns about the endorsement, though. While he has tremendous respect for Allen, Cancian said he worries that having retired general officers involved in political causes may prompt the White House to exclude top military leaders from the decision-making process, he said.

"In the White House, everything is political," Cancian said. "If they worry that deliberations might be leaked or people might go to work for the political opposition, then they just won't invite those people and they'll stick with the political appointees that they're comfortable with."

In some countries, general and flag officers are promoted based on their political leanings, he said.

Allen is the latest retired general officer to endorse a candidate throw his hat into the ring this election cycle. Retired Army Lt. Gen. Michael Flynn spoke in favor of Republican presidential nominee Donald Trump at last week's Republican National Convention in Cleveland.

One expert on civil-military relations fears that by endorsing Clinton, Allen could give the appearance that he is speaking for current senior military leaders.

"A man of his prominence and his rank can be interpreted to speak for the whole military community, retired and active duty," said Richard Kohn, who teaches military history at the University of North Carolina at Chapel Hill.

Kohn said he does not believe any retired military officer should ever endorse political candidates.

"They are in effect declaring themselves partisans and leaving the non-partisanship of the military profession and that's a different thing," he said.