By Judith MillerWriter/Contributing Editor, The Manhattan Institute/FOX News Contributor

The dramatic foiling of a year-long plot to blow up two New York City synagogues and shoot down military planes at an Air National Guard base in Newburgh, New York has important lessons for combating terrorism in America. First, it reinforces the New York Police Department's argument that militant Islamic terrorist threats to the United States may increasingly be homegrown.

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The foiled plot in New York demonstrates that the terrorist threat to America, and to New York in particular, did not end with Obama's election as president.

Law enforcement officials say they believe that at least three of the four accused were converts to Islam, that all four had been in prison. One of them was on parole. One official said that they may have met and perhaps been radicalized while attending a post-prison release rehabilitation program in Newburgh, some 70 miles north of New York City.

Second, a law enforcement official said that the disruption of the plot illustrates the importance of having police surveillance in place "at the right time and the right place" given how quickly the operational part of the planned attack unfolded. According to the complaint charging the three African-Americans and one Haitian-born immigrant with conspiring to use WMD in the United States, the men decided to get weapons to attack their targets at a meeting on December 5, 2008. This means that the plot went into high gear in less than six months.

Third, the incident demonstrates the importance of a smooth working relationship between the Federal Bureau of Investigation, which led the investigation, and the New York Police Department. In recent years, relations between the agencies have been strained over access to information in counter-terrorism cases and by other turf issues. But both Federal and local officials said today that cooperation had improved significantly since the appointment last December of a well-respected G-man, Joseph M. Demarest Jr., to head the FBI's powerful New York office. Both NY Police Commissioner Ray Kelly and Mr. Demarest were on hand at the press conference last night describing details of the alleged plot.

Fourth, the disruption of the attack depended in large part on information provided by a "confidential witness," an informant whom the FBI recruited six years ago and sent to Newburgh after pleading guilty in 2002 to criminal fraud and being sentenced to five years of probation. The complaint quotes a FBI official as saying that the information the informant provided during this and other investigations "has proven to be accurate and reliable" and has been "corroborated by other evidence."

Finally, while Washington is mired in debate about how and where Gitmo detainees should be held and/or tried, the foiled plot in New York demonstrates that the terrorist threat to America, and to New York in particular, did not end with Obama's election as president, but rather, remains alive and well. James Cromitie, the plot's alleged ringleader, is an American citizen and convert to Islam. Also known as "Abdul Rahman," Cromitie was released in 2004 after having served four years in prison for selling drugs in a school zone. To the best of law enforcement's knowledge, he had never met anyone from Al Qaeda or a terrorist group. Yet the complaint quotes him last November lamenting the fact that "the best target [the World Trade Center] was hit already." That left a strike at Iraq and Afghanistan-bound military aircraft and an attack on synagogues as the best fallback targets. "I hate those motherf***ers, those f***ing Jewish bastards," the complaint quotes Cromitie as saying. "I would like to get [to destroy] a synagogue."

Onta Williams, known as "Hamza," 33, had also served a year in jail in 2003 for possessing a controlled substance, believed to be cocaine, a law enforcement source said. Last April, the complaint says, he declared "in substance" that "they [the U.S. military] are killing Muslim brothers and sisters in Muslim countries, so, if we kill them here [in the United States]...it is equal."

The FBI supplied the alleged plotters with three mock "impromptu explosive devices" containing 30-plus pounds of phony C-4, which Cromitie placed on Wednesday night in cars parked in front of two synagogues, including the Riverdale Jewish Center. Had it been real, that much C-4 could have significantly damaged the building, which was scheduled to hold three services on Thursday morning at 6:05 am, 6:45 a.m. and 7:45 a.m.

Law enforcement officials say that the men were going to explode the IED's remotely by cell phone as they attacked Afghanistan and Iraq-bound aircraft taking off from Stewart International Airport in Newburgh. But the stinger missiles the informant had provided were, fortunately, as phony as the IED's.

All four men are presumed innocent until proven guilty, of course, and whoever winds up defending them will undoubtedly argue that that the informant egged the four men on and provoked them into staging the attack. There is still much we don't know about how and where the men met, how and where they were radicalized, and whether in fact their alleged violent tendencies were enflamed by the informant.

But the foiling of the plot seems at face value a clear success for the FBI and NYPD. The sense of vindication today is especially keen within the NYPD, which in 2007, released a 90-page assessment of the terrorist threat facing the nation. The study argued that the primary terrorist threat to New Yorkers--indeed, to all Americans--comes not from Al -Qaeda in Iraq or from the mountainous tribal region between Pakistan and Afghanistan, as the intelligence community in Washington asserted that same year in its national intelligence estimate. Rather, the NYPD concluded, the main terrorist threat was increasingly homegrown. While Al Qaeda remained a vital source of "inspiration and an ideological reference point," the study concluded, the more insidious terrorist threat came primarily from younger Muslim men between the ages of 15 and 35 who have no direct Al Qaeda connection, but who become radicalized by exposure to an "extreme and minority interpretation" of Islam.

That seems to be the case in this latest of the homegrown plots interrupted by the NYPD and the FBI.

Judith Miller, a Fox News contributor, is an award-winning writer and author, and an adjunct fellow at the Manhattan Institute. The author of several books, her latest is "The Story: A Reporter's Journey" (Simon & Schuster, April 7, 2015) now available in paperback. Follow her on Twitter @JMFreeSpeech.