Maine's Olympia J. Snowe has long thrived as one of the Senate's leading GOP moderates, but she has recently sided with tea partyers on high-profile votes involving Libya, the budget and the environment as she braces for a primary challenge from the right.
Such votes could help Mrs. Snowe fend off tea party foes who mock her as a "RINO" - Republican In Name Only - and hope to stop her bid for a fourth term next year.
Mrs. Snowe insisted she's been true to her moderate roots.
"I am who I am," Mrs. Snowe said. "I haven't changed."
Another test for Mrs. Snowe could come as Senate Democrats push for a vote on a GOP House budget plan that calls for deep cuts and privatizing Medicare. Democrats who see the plan as politically unpopular want to put Republicans like Mrs. Snowe on the hot seat.
She backed a motion by Kentucky Sen. Rand Paul, a tea party hero, to undercut President Obama's use of military force in Libya.
Mrs. Snowe joined nine Republican senators, most of them conservatives, supporting Mr. Paul's motion, but it failed, 90-10. Maine GOP Sen. Susan Collins voted for it, giving Mrs. Snowe political cover. Other moderates like Arizona Sen. John McCain opposed it.
Her vote was a protest against Mr. Obama's failure to consult with Congress on Libya, Mrs. Snowe said.
Mrs. Snowe backed Senate Republican leader Mitch McConnell's measure to ban the Environmental Protection Agency from regulating greenhouse gases. She said new regulations could hurt financially struggling manufacturers who have already made strides to curb emissions.
Mrs. Snowe also voted for a Republican House budget pact that included a ban on federal money for Planned Parenthood. Mrs. Snowe, a supporter of abortion rights and women's health issues, criticized the cuts before voting for the bill.
The ban was championed by conservatives who object to Planned Parenthood as the country's largest abortion provider, although federal law already bars the use of federal funds to perform most abortions.
Mrs. Snowe later voted against a resolution to ban federal funding for Planned Parenthood.
New England Republicans have long survived as centrists, touting fiscal responsibility while often siding with Democrats on social issues like the environment and abortion. But Mrs. Snowe has voted with her party 91 percent of the time in the new Congress, compared with just 69 percent in the previous Congress, a Washington Post voting database showed.
Mrs. Snowe, 64, is facing her first primary fight, after cruising to a third term in 2006 with 74 percent of the vote.
She wants to avoid the fate of Republicans swamped by last year's tea party surge such as former nine-term moderate Rep. Michael N. Castle, who was dealt a surprise defeat by tea party favorite Christine O'Donnell in Delaware's Senate primary.
"She is well aware of the fact that she's on the target list," said Mr. Castle, a Snowe ally. "She'll be ready for it."