Mitt Romney returned to the political stage Tuesday night in New Hampshire and warned fellow Republicans against a government shutdown, which he said would bring dire human and political consequences.

The 2012 GOP presidential nominee waded into the policy fight over possibly defunding President Obama's signature health-care law in the budget battle set to resume in September. Romney rejected a strategy proposed by leading congressional Republicans -- including Sen. Marco Rubio (R-Fla.), a leading Romney surrogate last year -- who are threatening not to pass a year-end budget bill if it includes funding for the health-care law.

"Emotion is understandably at play in Washington among some of our fellow Republicans," Romney said, according to his prepared remarks. "I badly want Obamacare to go away, and stripping it of funds has appeal. But we need to exercise great care about any talk of shutting down government. What would come next?"

Romney warned of soldiers not being paid, seniors fearing their Medicare and Social Security checks might stop, and FBI agents being forced off duty.

"I'm afraid that in the final analysis, Obamacare would get its funding, our party would suffer in the next elections, and the people of the nation would not be happy," Romney said.

Romney's speech came at a private GOP fundraiser before about 200 supporters in Wolfeboro, N.H., the lakeside vacation town where he and his family have a summer retreat. The event was closed to reporters, but Romney's aides provided a copy of his prepared remarks to reporters.

Romney's remarks were expansive -- from an economic and jobs picture he called "heartbreaking" to the civil war in Syria and turmoil in Egypt -- and amounted to a stinging indictment of the Obama administration.

On the economy, Romney said, "We have had five years of economic stagnation. It is inexcusable…I must admit, it has been hard to watch or read the news. What we feared would happen is happening."

Romney said the strife in Syria is "a tragedy" that he said could have been avoided had the Obama administration been more aggressive.

"It could have been a victory, for its people, for freedom, for America. Our leading from behind meant no real leadership, and into the vacuum rushed al Qaeda on one front, and Russia on the other. Tens of thousands of human beings have been slaughtered, and Iran's hand there may well become stronger than ever."

Romney also criticized the Obama administration for its handling of the nuclear threat, as Iran, North Korea and Pakistan advance their nuclear programs.

"Nuclear proliferation and the potential for nuclear terror have advanced, not retreated," Romney said. He added, "Russia modernizes its nuclear arsenal, and basks in the huge lead it has in its total nuclear arsenal of strategic and tactical nuclear weapons. And we -- we shrink our nuclear force and cut back on our missile defenses."

However, Romney singled out Secretary of State John F. Kerry for praise, saying he should be commended for his effort to bring peace to the Middle East. Romney called it "a success."

Romney, who has made clear he will not run for office again, mused about the choice before Republicans in selecting a presidential nominee in 2016. He urged Republican primary voters to "stay smart."

"Staying smart also means backing candidates that can win," Romney said. "I greatly appreciate the support the New Hampshire Republican voters gave me. I know that some of you may have actually lined up more with one of the other GOP candidates, but you gave me your nod because you felt I had the best chance of beating President Obama."

In 2016, Romney added, "there will only be one or perhaps two who actually could win the election in November. Think it through. Stay smart. Get behind those candidates."

Romney's visit to Wolfeboro was his first appearance on the political scene since losing the presidential contest last November. He raised money for the New Hampshire Republican Party, rewarding the state that helped propel him to the nomination last year. Ticket prices were $100 and up, and state Sen. Jeb Bradley, an early Romney supporter who is considering a challenge next year to Sen. Jeanne Shaheen (D-N.H.), emceed the event.

The fundraiser was held at a mansion on Lake Winnipesaukee where then-French President Nicholas Sarkozy stayed during a 2007 vacation. Donors nibbled from a raw bar of clams and oysters as Romney spoke on a deck overlooking the lakeshore, organizers said.

A handful of former campaign aides attended the event, including spokesman Ryan Williams, assistant Kelli Harrison and New Hampshire strategist Jim Merrill. Romney, who drove himself to the fundraiser, brought with him a wedding present for Merrill and his fiancé -- a luxury wooden punch bowl set.