Since the United States was attacked on 9/11, more than 2.3 million Americans have volunteered to go overseas to combat terror. But according to a new investigative report issued Wednesday by the Republican staff of the House Homeland Security Committee, overseas jihadists in Afghanistan and Iraq have plenty of company when it comes to trying to kill American soldiers.

According to the report, the Defense Department considers the U.S. homeland to be "the most dangerous place for a G.I. outside of foreign warzones," and the top threat faced by American soldiers at home "is from violent Islamist extremists." These radicals are penetrating U.S. defenses by enlisting in the U.S. armed forces.

"A significant and growing number of military personnel, such as alleged Fort Hood mass murderer Army Major Nidal Malik Hasan, pose a serious danger to their brothers and sisters in arms who wear the same uniform," the report concluded. U.S. authorities have detected "at least 33 threats, plots and strikes against U.S. military communities since 9/11." Seventy percent of these plots against military targets have occurred since 2009.

The report was issued shortly before an unusual joint hearing held Wednesday by the House Homeland Security panel, chaired by Rep. Peter King (R-NY), and its Senate counterpart, chaired by Sen. Joseph Lieberman (D-CT).

While there appeared to be broad, bipartisan agreement between King and Lieberman about the jihadist threat, the Obama Administration and congressional Democrats appeared to take issue with the premise of the report – particularly the evidence it marshaled demonstrating that in case after case, the people targeting the soldiers were radicalized Muslims.

Assistant Secretary of Defense for Homeland Security Paul Stockton warned the committee not to use "imprecise terminology that may cause confusion and may unjustifiably give credence to the falsehood -despite our best intentions - that we are waging a war against Islam."

The ranking member of the House committee, Rep. Bennie Thompson, D-Miss., suggested that the hearing was grounded in stereotyping innocent Muslims, stating that "[a] congressional hearing that identifies one religion as a likely threat within the military is not only inaccurate but unwise."

But no one could possibly conclude that the committee's work is grounded in anti-Muslim stereotyping. "At least 6,024 U.S. service members who declared Islam as their faith have served honorably in overseas war deployments since the 9/11 attacks, and 14 Muslim-Americans have been killed in action," the staff report said. "We honor these American heroes, four of whom are buried at nearby Arlington National Cemetery, for making the ultimate sacrifice in service of our nation."

But "a particularly insidious aspect of the homegrown terror threat remains radicalized troops who target their fellow brothers and sisters in arms, without regard to their faith," the report stated.

It says the Obama Administration's muddled approach to Islamist terror is illustrated by its handling of the Fort Hood massacre and the June 1, 2009 murder of Pvt. William Long at a Little Rock, Ark. military recruiting center by a radicalized Muslim. The administration has refused to acknowledge that either crime is an example of violent Islamist extremism, and the soldiers killed and wounded in the shootings "have not received Purple Heart medals, despite pleas by their survivors that their loved ones fell in the line of duty," according to the staff report.

The administration's reluctance to discuss radical Islam's role in targeting the military continued at Wednesday's hearing. Watch here as the DoD's Stockton refuses under questioning from Rep. Dan Lungren (R-CA) to acknowledge that al-Qaida is engaged in "violent Islamist extremism."

Read the House Homeland Security Committee's report on Islamism in the military here.