WASHINGTON - Fresh voices in the U.S. Senate are speaking loudly on foreign policy, a new generation of Republicans and Democrats who reflect a war-weary nation cautious about America's next moves.

Sens. Kelly Ayotte of New Hampshire and Rand Paul of Kentucky stand on either side of the growing divide in the GOP, pitting those who favor more robust U.S. engagement overseas against an isolationist's deficit-driven concerns about the cost of foreign entanglements. Ayotte, a self-described Ronald Reagan Republican, is moving ahead with a new batch of sanctions against Russia in retribution for the annexation of Crimea and to send a clear signal to Moscow about further aggression.

"We're essentially dealing with a former KGB colonel," Ayotte said in a recent interview about Russian President Vladimir Putin. "He will only respect strength and doesn't respect accommodation."

Paul, for his part, voted against providing $1 billion in loan guarantees to cash-poor Ukraine and punishing Russia for its brazen moves last month. He raised concerns that the aid would have "the perverse impact of using American tax dollars to reward Russia." Paul repeatedly has challenged fellow Republicans and the Obama administration over National Security Agency surveillance, the use of drones, and spending on foreign aid and wars.

Committee leaders typically get the coveted spots on the Sunday-morning talk shows, the standard that says a senator has arrived. When the topics are global hot spots like Ukraine, Afghanistan, Syria, and Iran, TV hosts are turning to a new group of senators - young, studious, and with just a few years on the job. These lawmakers offer more nuanced views as the Cold War's clarity has been supplanted by a global war on terror against an array of faceless enemies.

Sen. Chris Murphy, a Connecticut Democrat, joined Paul last year in opposing arms for Syrian rebels, but was an early proponent of aiding Ukraine and imposing penalties on Russia. Virginia Democrat Tim Kaine has focused on Afghanistan as the U.S. draws down its military forces after more than a decade of war. At the same time, he has established a bipartisan Senate group of about 10 to change how presidents consult with Congress on sending the military into war.

For members of the new generation, which also includes Sen. Marco Rubio (R., Fla.), the world view is shaped by the terror attacks of Sept. 11 and the long conflicts in Iraq and Afghanistan.

The boyish Murphy, who at 40 is the youngest member of the Senate, says he ran for Congress in 2006 because he was outraged over the Bush administration's disastrous policies in Iraq. A member of the post-Vietnam generation, he sees limits to the "blunt instrument of military force" and scoffs at the notion that the United States can simply pivot toward one region.

"We're in a world today where doctrine doesn't serve us very well," Murphy, who was elected to the Senate in 2012, said in a recent interview. "I know there are a lot of people who think there should be clear, consistent lines that guide us. I'm not sure that black-and-white-world exists any longer."

Murphy and Paul, 51, serve on the Foreign Relations Committee; Kaine serves on both the Armed Services and Foreign Relations panels. Ayotte, 45, a member of the Armed Services Committee, has replaced former Sen. Joe Lieberman, a Connecticut independent, in the ad hoc group known as the Three Amigos with Sens. John McCain (R., Ariz.) and Lindsey Graham (R., S.C.) on defense and foreign policy.

"It's my mission now to try to get these newer people engaged in foreign policy issues," said McCain, 77. "There's a very, very big vacancy."

Ayotte says her foreign-policy education comes from hearings and travel overseas, including a recent congressional trip to Ukraine, Afghanistan, and Israel. She left no doubt about her worldview.

"We can think that things that happen overseas are just going to stay overseas," she said, "but I think what 9/11 taught us is things obviously that happen in other countries can really come back to bite America."

Kaine, 56, matches his political resume - former Virginia governor and Democratic National Committee chairman - with the real-world experience of working with Jesuit missionaries in Honduras.

"Some people say we've got to be the indispensable nation," Kaine said in a recent interview. "I just want to be the exemplary nation. Indispensable sounds like you're trying to put your nose in everybody else's business."

Kaine is working with McCain and other senators on a long-term effort focused on the 1973 War Powers Resolution, often ignored by presidents of both parties, and replacing it with a new law that requires a congressional vote within 30 days on any significant armed conflict.

Within that debate is the Authorization for the Use of Military Force, the law that has given the president extensive power, including authorizing lethal drone strikes.

Kaine said he spoke to Obama about it in August. In practical terms, Kaine said, he understands that it will take a year or two, if not more, to resolve the issue that goes to the heart of the constitutional authorities of the commander in chief and the legislature.