Yesterday during an open hearing on the evolving NSA surveillance scandal, Democratic Senator Jeff Merkley (OR) grilled NSA Director Gen. Keith Alexander on the program responsible for collecting the communication data of millions of Americans. In one specific back and forth, Merkley held up his cell phone to challenge Alexander, asking, "Here - I have my Verizon phone, my cell phone. What authorized investigation gave you the grounds for acquiring my cell phone data?"

It's a question being asked not only by politicians, but by everyday Americans, as well, who fear the government has surpassed its limits in breaching the privacy of its citizens.

In a rather heated interview on Thursday's America's Newsroom, Martha MacCallum questioned Rep. Peter King (R-NY), an outspoken advocate of the NSA and its PRISM program.

"I'm pretty much familiar with the entire program, and I support it ... I think the program is absolutely essential," he told her, adding that there's "absolutely nothing unconstitutional about it" and we should "thank God every day that this is in effect."

King credits the agency and the same data collection now being criticized with preventing the 2009 subway attack in New York City.

"I was on the ground in 2009 that Sunday evening," he said. "...Thousands of New Yorkers would have been incinerated in the subway system the next day if this wasn't in place."

MacCallum used the Boston bombing as what she called a "tailor made example" of a time when the government could have, and perhaps should have, engaged in more surveillance ... and didn't. "Why would these brothers have been able to protect their privacy when it appears so many others [cannot]?" She refused to back down when King responded, saying that there's no indication that any plotting was done through phone or email communications.

"Are you telling me that there'd be a judge where, if we went to him and said, the Russians alerted us to these guys, and you know, we can't find anything on them, but can we just keep looking at their phone stuff?' That judge is gonna say 'no'?!"

"Yes, I don't see that going through," King replied, as Martha cut in, saying, "Really ... that's disturbing..."<

"Just so you know, to this day, there's still no proof even now ... of foreign terrorist connections," King continues, "and until you can prove that, you can't use [PRISM] ...So what you're saying is [actually] it proves how much American citizens are being protected, sometimes even at the risk of our own safety."

"No, I think it proves that it's not efficient, that we're gathering so much information that we're not focusing on the right things," she rebutted.

Watch the full, fiery debate above.