WASHINGTON — In a nation weary of war, yet alarmed by the prospect of an emerging threat, President Barack Obama’s plan to strike Islamic State militants is ruffling the usual left-right politics in several races that will decide control of the Senate.

Republicans who have hammered the president on a variety of issues for months have tamped down their rhetoric and, frequently, are avoiding taking a clear stand on his proposal. Some of the nation’s most endangered incumbent Senate Democrats, meanwhile, have expressed skepticism to portions of Obama’s plan, saying they fear a new plunge into a new Middle East war where supposed allies can become enemies.

Others want to talk about something else, or are trying to avoid talking about the issue at all.

The complexities, leading to mixed and cautious responses from both sides, mean the issue might not matter much at all come Election Day, when Republicans need a net gain of six seats to take control of the Senate.

“I’m having a hard time seeing this as a game-changer,” said William A. Galston, a Brookings Institution scholar and former Clinton White House adviser. “A lot of people who would have said ‘hell no’ to the president’s speech were cheering him on.”

Republicans have made attacking Obama and his policies the cornerstone of their Senate campaign, especially as they target Democrats in states the president lost in 2012. They had in recent days stepped up their attacks on the president’s foreign policy, hoping to further tie vulnerable Democrats to an unpopular leader.

Despite that rhetoric, several GOP Senate candidates appear wary of taking detailed positions on the president’s proposal to fight Islamic State militants with air strikes and U.S.-armed Syrian rebels, but not American ground troops, since he laid it out in a televised speech Wednesday night.

New Hampshire Republican Senate nominee Scott Brown, a former senator from Massachusetts, sharply criticized Obama’s leadership in an interview Friday. But he declined to say whether he would vote to authorize more military intervention in the Mideast.

“I would need to listen to the generals on the ground and get their input and guidance as I have in the past,” he said. “When you’re … making a decision to send people into harm’s way, you need to have all the facts and I don’t have those facts.”

In North Carolina, Republican Senate nominee Thom Tillis said the militants “are growing stronger each day because of President Obama’s failed foreign policy and lack of leadership.”

When it comes to combatting the militants, “no option should be left off the table,” said Tillis, who faces first-term Democratic Sen. Kay Hagan. Yet when asked about Obama’s proposal to arm Syrian rebels fighting a three-way war against both Syrian President Bashar al-Assad and the Islamic State group, also known as ISIS, Tillis’ campaign said he “has reservations about sending arms that could be seized by ISIS terrorists.”

Tillis tried to turn the focus Friday away from Obama’s proposal and toward the rise of the Islamic State group, which has killed hundreds of civilians in Syria and Iraq — including two American journalists beheaded on camera. Obama and Hagan, the Tillis campaign said in a statement, “have never had a strategy to eliminate ISIS, and they still don’t have one.”

It’s an allegation Hagan, seeking re-election in a state Obama won in 2008 but lost four years later, strongly disputed. Her campaign cited an April 2013 hearing at which Hagan asked, “Is there a risk that the violence in Syria will spill across the border into western Iraq and strengthen al-Qaida in Iraq?” The group evolved into the Islamic State.

The same sort of shift has taken place in Colorado, where Democratic Sen. Mark Udall and his Republican opponent, Rep. Cory Gardner, have said in so many words that they support the Obama approach — air strikes and armed Syrian rebels, but no U.S. combat ground troops.

“I will not give this president, or any other president, a blank check to begin another land war in Iraq,” Udall said. Added Gardner, “I agree with the president’s decision to authorize airstrikes.”

In place of any disagreement on the policy, Gardner has instead slammed Udall for what he sees as the administration’s slow response to the danger and his comment last weekend that the Islamic State militants are not “an imminent threat” to the United States, although federal law enforcement officials had said the same thing.

Still others are trying to avoid such questions all together.

Republicans GOP Rep. Tom Cotton, running for Senate in Arkansas, said Obama “still hasn’t laid out a real strategy to defeat the Islamic State.” But Cotton didn’t offer any specific stands for or against the president’s proposals.

Cotton’s opponent, incumbent Democrat Mark Pryor, issued a brief statement this week generally supporting tougher action against the Islamic State group, without mentioning Obama’s name. It read similar to the words from Democratic Sen. Mary Landrieu of Louisiana.

Both Democratic senators are seeking re-election from Southern states where Obama lost badly in 2012. Both campaigns were asked Friday by The Associated Press for an interview with the senators to talk about the president and his plans to fight the Islamic State group, and neither responded.

CHARLES BABINGTON, Associated Press
NICHOLAS RICCARDI, Associated Press__

Riccardi reported from Denver. Associated Press writer Rik Stevens in Concord, New Hampshire, contributed to this report.