ANCHORAGE, Alaska (AP) — A Twitter admonishment from President Donald Trump didn't seem to faze U.S. Sen. Lisa Murkowski, a moderate Republican whose vote is key for the GOP's hoped-for health care overhaul.

The Alaska lawmaker and U.S. Sen. Susan Collins of Maine were the only two Republicans who on Tuesday opposed moving forward with allowing debate on GOP legislation to repeal much of the Affordable Care Act, the health care law passed under former President Barack Obama. Vice President Mike Pence stepped in to break the 50-50 tie.

"Senator @lisamurkowski of the Great State of Alaska really let the Republicans, and our country, down yesterday. Too bad!" Trump tweeted Wednesday.

Murkowski defended her vote. She repeatedly has expressed concerns about deep Medicaid cuts in the GOP bill. She's also has called for a bipartisan process to address shortcomings of the current health care law and to stabilize individual markets.

"You know I am comfortable with the decision that I made yesterday in working to advance Alaska's interests and working today to do the same," she said Wednesday.

"I don't' really follow Twitter that much," she added.

Alaska's senior senator holds a unique place in the health care battle, given the vast state's remote location and small population. A quarter of Alaska's 740,000 residents are covered by Medicaid, which Gov. Bill Walker, an independent, expanded as part of the Affordable Care Act to include more lower-income people. Only about 20,000 Alaskans get insurance on the individual market, resulting in a tiny pool across which insurers can spread costs. The number of insurance companies writing individual policies in Alaska has dropped from five to one.

Before this week's vote, Murkowski said she made it clear to Trump that her first commitment was to Alaskans.

"There may be pressures that come at me from, whether it's the president or others, there may be those who say, 'As a Republican, you need to stand with the president without question," she said last week. "But my commitment is to try to do the best that I can for the people that I work for."

Murkowski, 60, is in her fourth term representing the nation's largest state and she chairs the powerful Senate Energy Committee. Murkowski, whose father served as a U.S. senator and governor, survived a near-death political experience in 2010 when she lost her party's primary to tea party favorite Joe Miller but retained her seat as a write-in candidate. Last year, she again defeated Miller, who ran then as a Libertarian.

"The senator has lied numerous times to Alaskans about where she stands on repeal. This is nothing new to her constituents, as she has done the same on the question of life, homosexual marriage, and many other issues," Miller said in an email to The Associated Press. "Murkowski is a poster child for all that is wrong with America's corrupt political system, and remains an embarrassment to the State of Alaska."

However, he said another challenge to Murkowski in 2022 seems "unlikely," citing what he calls voting irregularities in the state.

Tuckerman Babcock, state GOP chairman, urged Republicans to write or call Murkowski. "We do expect the Republican team to keep its promise to repeal Obamacare," he said. Babcock was "dismayed" by her vote Tuesday, he said.

Judy Eledge, president of the Alaska Republican Women's Club, slammed Murkowski for refusing to vote on an outright repeal. Eledge said club members, who have been writing Murkowski, aren't happy about the senator's decision to buck the party stance, but said they're used to it. They've never been able to depend on her for a conservative Republican vote, according to Eledge.

"She normally doesn't disappoint. She normally votes with the Democrats," Eledge said.

Malena Marvin recently finished a round of chemotherapy for breast cancer, treatment she was able to receive through insurance under the current health care law.

Marvin, an independent who lives in a small southeast Alaska fishing community of Petersburg, said Murkowski has been sensitive to feedback from constituents. In an interview before this week's vote, she said she was glad that Murkowski has stood up to Republican Party leaders and to Trump on the issue.

"I think that takes a lot of courage, and I think we should all be grateful for her boldness," she said.

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Associated Press writers Becky Bohrer in Juneau and Mark Thiessen in Anchorage contributed to this report.