WASHINGTON — Republican senators poised to lead major committees when the GOP takes charge are intent on pushing back many of President Barack Obama’s policies, setting up potential showdowns over environmental rules, financial regulations and national security.

The all-GOP Congress – Republicans also have a commanding majority in the House – gives the powerful Senate committee heads a newfound opportunity to steer legislation and help shape the national debate.

With Republicans winning control of the Senate in the November election, all the committees will get new leaders, though all have been around for years.

The heads of the 13 major committees and Veterans’ Affairs are some of the most senior members of the Senate. Three are octogenarians and four are in their late 70s. Only one new leader will be a woman; Alaska Sen. Lisa Murkowski is in line to take over the Energy and Natural Resources Committee.

A look at the powerful senators and their issues:

AGRICULTURE

Kansas’ Pat Roberts, 78, will consider renewal of child nutrition programs that have been pushed by the White House and expire next year. Roberts has criticized efforts to make school lunches healthier, calling for studies on the costs of the program and economic impact on schools.

Roberts has been a recent dissenter on the normally bipartisan panel, voting against the five-year farm bill that Congress passed in May. Roberts supported the bill’s boost in crop insurance for farmers but said other subsidies needed more changes. He called the entire bill “a look in the rear-view mirror.”

Like his Republican counterparts in the House, Roberts has championed cutting back spending for food stamps, saying the farm bill’s estimated cut of $8 billion over 10 years was insufficient.

Roberts held the gavel of the House Agriculture Committee 20 years ago and during his tenure he helped write the 1996 farm bill.

APPROPRIATIONS

The gavel of the powerful panel responsible for drafting approximately one-third of the federal budget will return to Mississippi’s Thad Cochran, who turned 77 in December and was just re-elected to a seventh term.

Cochran was in charge during the last two years of the previous GOP majority and was a driving force behind more than $100 billion in funding to help Gulf Coast states recover from Hurricane Katrina. He was also a big practitioner of earmarks, those home-state goodies such as highway projects, economic development grants and university research dollars.

GOP leaders have banned earmarking, but Cochran is sure to back Navy shipbuilding efforts. Ingalls Shipbuilding in Pascagoula, which makes a variety of Navy ships such as modern destroyers, is Mississippi’s largest private employer.

Republicans are expected to use the 12 spending bills to challenge Obama on policy issues, such as health care, financial services, immigration and the environment.

ARMED SERVICES

Leading the committee has been a long-sought goal for 78-year-old John McCain of Arizona, the former Navy pilot, Vietnam prisoner of war and two-time presidential candidate who lost to Obama in 2008.

McCain, who has hinted he might seek a sixth term in 2016, stands as one of Obama’s fiercest critics on national security, casting the administration as weak and ineffective in countering threats overseas. He has repeatedly called for arming and training moderate Syrian rebels and favors more U.S. forces in Iraq to battle Islamic State militants.

McCain has been critical of Pentagon contracting. Increased examination of defense manufacturers and acquisition policy is certain. The Pentagon can largely forget about scrapping the A-10 Warthog aircraft, which McCain heavily favors, and can expect close scrutiny of the costly F-35 fighter jet.

BANKING, HOUSING AND URBAN AFFAIRS

The wily Richard Shelby, 80, makes a return tour as head of the committee. High on his agenda will be changes to the financial overhaul law enacted in response to the 2008 crisis, known as Dodd-Frank. The 2010 law that brought stricter regulation of banks and Wall Street has been a burr in the side of Republican lawmakers, and the GOP-controlled House has passed numerous bills to unwind it.

Sen. Mitch McConnell, R-Ky., the next majority leader, put it plainly at his day-after-the-election news conference: “The Banking Committee is certainly going to look at Dodd-Frank.” The big banks, he said, “are doing just fine under Dodd-Frank. The community bankers are struggling.”

Besides bank rules, the committee under the Alabama senator also may focus on curbing the authority of the Consumer Protection Financial Bureau over auto lenders and credit card companies. The bureau was created by the financial law.

Also likely to get committee attention is legislation to reshape the housing finance system and wind down mortgage giants Fannie Mae and Freddie Mac.

Shelby succeeded as head of the panel from 2003 to 2007 in blocking bank regulation proposals.

BUDGET

In a surprise, Wyoming’s Mike Enzi will become chairman of the Senate Budget Committee after Jeff Sessions of Alabama stepped aside. Sessions had been the top Republican on the committee the past four years.

Enzi, 70, said he will work to craft a budget “that cuts spending, targets executive overreach and reduces the size of government.”

He will be called upon to craft a budget framework that could serve as a template for follow-up legislation to repeal Obama’s health care law and, perhaps, tackle expensive benefit programs such as Medicaid and food stamps.

COMMERCE, SCIENCE AND TRANSPORTATION

South Dakota’s John Thune, 53, faces a heavy workload – reauthorization of the Federal Aviation Administration and Amtrak, net neutrality and transportation.

The committee will have to address the auto safety portions of the highway bill in the aftermath of General Motors faulty ignition switch recalls, now linked to more than two dozen deaths, and the Takata air bag recalls, also linked to several deaths. Proposals to toughen federal oversight of the auto industry are likely. Some lawmakers have called for eliminating the $35 million cap on how much the government can fine automakers in such cases.

ENERGY AND NATURAL RESOURCES

An energy policy expert from an energy-producing state, the 57-year-old Murkowski wants to unlock as much of America’s energy as safely possible.

Murkowski has argued for opening up the Arctic National Wildlife Refuge for drilling, as well as Alaska’s offshore, and has opposed regulations that block energy production. She believes EPA regulations to curb coal-fired power plant pollution to deal with global warming will threaten the reliability and raise the costs of electricity.

She supports exporting U.S. natural gas and has led the charge on pressuring the administration to lift restrictions on exports of crude oil. She has backed the immediate approval of the Keystone XL oil pipeline, which McConnell has said will be first on the new agenda.

Murkowski, unlike others in the GOP, believes global warming is happening and that Alaskans are already experiencing the effects of rising water temperatures and thinning ice.

ENVIRONMENT AND PUBLIC WORKS

The likely ascent of Oklahoma’s James Inhofe, 79, represents one of the biggest sea changes on a Senate committee with Republicans in charge.

Inhofe, one of Congress’ most vocal deniers of the scientific consensus of climate change, wrote in a 2012 book that global warming was “a hoax.” He will replace Californian Barbara Boxer, who introduced climate change legislation in 2009 and was an ally of the environmental community and Obama.

Inhofe, by contrast, is a thorn in the side of the Environmental Protection Agency and has argued that more regulation will kill the economy and jobs. Inhofe has called on the EPA to abandon stricter rules on refinery air pollution and to reject their own scientists’ recommendation to tighten a standard for the main ingredient in smog. Inhofe is likely to boost oversight of the agency and try to thwart its agenda at a time when Obama wants to shore up his climate legacy.

FINANCE

The 2010 health care law is in the GOP’s crosshairs, and Utah’s Orrin Hatch, 80, is likely to use his position to take the first step at chipping away at it.

Hatch has called the law’s tax on medical devices “stupid” and is determined to roll it back. He is likely to gain some Democratic support for the effort.

Hatch could be a free-trade ally for Obama if the president pushes more trade agreements.

Overhauling the nation’s complicated tax laws also is a priority for Hatch. But it’s a heavy lift.

Administration officials say Obama will offer new specifics in the coming year on how he would like to reshape corporate taxes, which now feature the highest rate in the industrialized world. But bridging the divide between Republicans and Democrats on major tax legislation would require a level of bipartisanship that has largely been absent during Obama’s first six years as president.

Hatch has worked with Democrats in the past; his friendship with the late Sen. Edward Kennedy of Massachusetts is legendary. Hatch will need to work with Democrats again if he is to advance an overhaul of the tax code.

FOREIGN RELATIONS

Tennessee’s Bob Corker, 62, has criticized Obama’s foreign policy as tepid in dealing with Russia, Libya and Syria. Like several other Republicans on the committee, Corker has deep reservations about the administration’s negotiations with Iran over its nuclear program. Some Republicans have said the GOP will push new penalties this month that target Tehran.

Secretary of State John Kerry has asked Congress for new war powers in the fight against the Islamic State group. Corker has raised the possibility that he could work with the administration on the issue.

Obama’s ambassadorial picks and other nominees would face a rough outing before the committee.

HEALTH, EDUCATION, LABOR AND PENSIONS

Tennessee’s Lamar Alexander, 74, is a former education secretary under President George H.W. Bush, governor and president of the University of Tennessee.

A lawyer by trade, he helped form a corporate childcare company in the private sector. Alexander said he wants to fix President George W. Bush’s No Child Left Behind education law that’s been due to be renewed since 2007 and update the Higher Education Act.

He’s called the health care law a “historic mistake” and supports repealing it. He’s also said modernizing the National Institutes of Health and Food and Drug Administration is a necessity, and he is seeking to examine the FDA’s process for drug and device review. On workers’ issues, he’s sought to turn the National Labor Relations Board into what he says is more of an umpire role.

JUDICIARY

A farmer, not an attorney, Iowa’s Charles Grassley, 81, has been on the Judiciary Committee since his 1980 election to the Senate. But this will be his first stint as its chairman.

In that post, many expect him to continue his long-running interest in protecting whistle-blowers who reveal details of alleged fraud by government contractors and others. He’s also expected to continue oversight of programs like the Justice Department’s bungled “Fast and Furious” operation, under which federal agents lost control of guns they were tracing to Mexican drug lords. Many also expect him to work on legislation easing federal regulations on businesses.

Grassley opposed last year’s Senate-approved bipartisan immigration bill, arguing that it needed to do more to secure the country’s borders before granting legal status to people in the U.S. illegally. He’s also pressed for more information about the National Security Agency’s ability to gather information on Americans, though he’s cautioned that the agency must be able to protect national security.

A decade ago, Grassley spent time as chairman of the Senate Finance Committee and played a role in winning approval of President George W. Bush’s 2001 tax cuts and the 2003 addition of prescription drug benefits to Medicare.

HOMELAND SECURITY AND GOVERNMENTAL AFFAIRS

Wisconsin’s Ron Johnson, 59, has been a tough questioner of administration officials about the deadly 2012 attack on the U.S. diplomatic outpost in Benghazi, Libya. The question will be whether the panel’s Permanent Subcommittee on Investigation opens another Benghazi inquiry in Congress as well as other reviews of the Democratic administration.

Under the leadership of Delaware Democrat Tom Carper, the committee focused primarily on the internal workings of the sprawling Homeland Security Department, including low morale ratings from rank-and-file employees and contracting issues.

Johnson has focused on those rankings in the past and led an investigation of complaints from whistle-blowers about the department’s former acting inspector general. His report, co-authored with Missouri Democrat Claire McCaskill, prompted DHS Secretary Jeh Johnson to suspend the former top internal investigator.

While the committee has addressed immigration issues in the past, senators on this panel have not taken as prominent a role as their counterparts on the Senate Judiciary Committee. In the coming months, however, any administrative changes put in place by Obama are almost certain to be reviewed.

VETERANS’ AFFAIRS

Georgia’s Johnny Isakson, 70, has stressed mental health needs of veterans and voted in favor a bill to provide two-year funding for veterans’ benefits, so veterans would continue to receive benefits even in a government shutdown.

Aides say Isakson’s priorities as chairman would include oversight of the new Veterans Access, Choice and Accountability Act of 2014, which was approved this past summer in response to a scandal over long wait times for veterans seeking health care and falsification of records to cover up delays.

Isakson strongly supports a provision in the law that makes it easier for veterans to seek Department of Veterans Affairs-paid care from local doctors. Bringing competition into the VA health care system will improve services, he says. Isakson also said the new law provides an opportunity for the VA to assess the quality of it leadership and management, and said underperforming executives and managers should be fired.

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Associated Press writers Andrew Taylor, Kimberly Hefling, Joan Lowy, Alan Fram, Marcy Gordon, Matthew Daly and Alicia Caldwell contributed to this report.