Christopher Harmer, a senior naval analyst for the Institute for the Study of War, said that such questioning of America makes the world more dangerous.
"Never since before World War II have our enemies feared us less, never have our allies trusted us less," he said. Keeping the peace "doesn't work unless our enemies fear us and our allies trust us. Right now that fear and trust is in question."
House Intelligence Committee Chairman Devin Nunes, R-Calif., said, for example, that intelligence agencies warned two years ago that radical Islamic terrorism could "spread like wildfire" and needed quick attention, but said the Barack Obama administration essentially ignored it.
"We were warned," he said. "But the administration was out pretending like the wars were over al-Qaida is on the run, they've been decimated, ISIS is the JV [junior varsity] team," he said.
"The bottom line is that ISIS and al-Qaida are larger and have more followers than ever before." He added, "We don't have a strategy in place to really go after this problem because the political leadership in this country decided that wars could end just by someone saying, 'Well the war's got to be over.'"
Harmer said questions about U.S. commitment appear to be emboldening Iran and the terrorism that it sponsors.
"Iran is morphing into a terrorist superpower." He asserted that America has aided that by easing sanctions against it in a recent nuclear deal approved by the Obama administration.
Harmer said Iran is arming terrorists worldwide and has been developing missiles that could help its avowed goal of destroying Israel. "If we do not prevent it, the current leadership of Iran will attack Israel. It's just a matter of time."
He added, "We should increase sanctions on Iran. We have the ability to reduce their economic capacity to support terror. We are not doing that. We are doing just the exact opposite."
Harmer added, "You have to be well armed, you have to be credible. And right now because we are less well armed and less credible, our enemies are taking advantage."
Stewart, a former Air Force pilot, said one reason the world sees America being less willing to protect the peace is that in 2003, the U.S. had 158 fighter squadrons. "This year there are 57. And of those 57, about half of them are not combat capable."
He added, "The assumption has always been that we have the mightiest military in the world. I want you to know I still believe that is true. But our military is standing on the edge of a knife with capability."
Nunes outlined other areas that pose perhaps the greatest threats to world peace.
Russia in recent years has annexed the Crimea, invaded the Ukraine and Georgia and launched air attacks on U.S.-backed fighters in Syria, Nunes noted.
He said China is building small islands that essentially act as permanent aircraft carriers in the ocean, is building 351 navy ships and is "stealing hundreds of billions with cyber-espionage."
He said North Korea has been testing ballistic missiles, has numerous nuclear weapons and has been saber rattling against America.
Atsuyuiki Oike, Japan's deputy chief of mission in its U.S. embassy, said "the role of the United States is very much indispensible" in securing peace and freedom in Asia amid such threats.
"I believe what we have to do is make clear that we have to respect the rule of law," he said. "And if you do something contrary to that, you have to pay a high cost for that. That has to be made very clear" and America has the economic and military clout to do that.