Between January and May 2015, fully 41 Muslims living in the United States were caught allegedly trying to join the terror group ISIS.

PJ Media first reported the development, while pointing to the White House's failure to recognize the full threat from the Islamist organization that rapidly is expanding in the Middle East.

"The arrest of two southern California men last week who were planning to travel to Syria to join the Islamic State brings the number of U.S.-based individuals involved in international terror-related cases this year to 40," PJ Media reported.

Read "Stealth Jihad: How Radical Islam is Subverting America without Guns or Bombs" and discover that the next major Islamist attack on America already is under way. By Robert Spencer.

TRENDING: Undercover journalist turns the tables, sues Planned Parenthood for defamation

Monday's arrest of a Houston-area man, Ashe Abid Khan, brings the total to 41.

Jihad Watch reported: "This number highlights the metastasizing Islamic terror threat in the American homeland. At the current pace, by the end of June, halfway through 2015, the number of cases will exceed the number from the past two years combined, at 48."

ISIS and al Qaida affiliates have repeatedly called on members to launch assaults on U.S. soil, at one point even releasing a "kill list" that included the names, addresses and photographs of various American military members.

After the recent Garland, Texas, attack – foiled – at the "Draw Muhammad" contest, ISIS operatives claimed to have 71 members in 15 states in America.