Only 3 Senate Republicans aren't defending Trump from the impeachment inquiry. Here's why. - NBC News

For those Senate Republicans who are refusing to condemn the House-led impeachment inquiry, three may be the loneliest number.

While a resolution denouncing the House Democrats' fast-moving probe hasn't received a vote, GOP Sens. Mitt Romney of Utah, Susan Collins of Maine and Lisa Murkowski of Alaska declined to sign on as co-sponsors — the only ones out of 53 Republicans — leaving the door ajar to the possibility that they could vote to convict President Donald Trump if impeachment moves to its trial phase in the Senate.

But unlike the blowback Romney and Collins have faced for breaking with the party's defense of the president, Murkowski could end up seeing her part in this micro-rebellion embraced by voters in her state. Experts on Alaska politics told NBC News that the state tends to reward an independent streak in its politicians.

"As far as supporting or opposing the president, we support individualism and we support individual freedom of expression. And that goes for our politicians, too, whatever party they are," said Tuckerman Babcock, who retired as the chairman of the Alaska GOP last year. "Republicans here may disagree with her on certain things, but I can say safely that they respect her independence of judgment."

In other words, Murkowski can fall out of line with Trump — but not fall out of favor with Republican voters in her state.

Murkowski voted against the Senate's Trump-backed effort to repeal Obamacare in 2017, but later came out in support of repealing the Obamacare individual mandate. She voted against the confirmation of Supreme Court nominee Brett Kavanaugh but backed Trump’s tax cut bill. And she votes in line with the president's position on bills about 75 percent of the time, according to a FiveThirtyEight tally.

Nov. 5, 201901:33

Murkowski also benefits from not being up for re-election for three years and from the strong financial backing she has always received from Alaska Native corporations and interest groups, an influential Alaska constituency.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings.

"These things give her the leeway to vote with her heart so often," Chanda Meek, a professor of political science at the University of Alaska-Fairbanks who studies Alaska politics, told NBC News.

On the other hand, Murkowski's political rivals point out that across her three Senate races (in 2004, 2010 and 2016), she has never won a majority of the vote — a fact they say signals that there will always be room for a more conservative candidate to mount a challenge when she is up for re-election.

But even those adversaries admit that the unique nature of Alaska politics is likely to enable Murkowski to follow the facts on impeachment — even if the Republican voters oppose it.

"When it comes to the rank and file, I believe strongly that impeachment is looked upon with great disdain and as a reflection of how the system is totally broken," said Joe Miller, a conservative attorney who ran against Murkowski in 2010 and the 2016. "Because she's so clearly outside the Republican mainstream (her) position is secure because the Republican Party here is just so broad."

Murkowski has said that she wouldn't support the Sen. Lindsey Graham's resolution condemning the impeachment inquiry because "it's not the Senate's role to dictate to the House how to determine their own rules."

Her office repeatedly declined to answer questions from NBC News about her position, pointing instead back to the senator's previous statement about not signing on to the resolution.

"From the get-go, Speaker Pelosi and House Democrats have handled this impeachment inquiry poorly, from closed-door hearings and leaked information to the outright abandonment of decades of established precedent on due process for the accused," Murkowski said in that statement. "A serious lack of transparency will hardly build public trust or credibility for the House's actions. As awful as their process is, the formal impeachment inquiry lies in the House, and it's not the Senate’s role to dictate to the House how to determine their own rules."

That statement differed starkly with Romney’s sharply worded criticism of Trump's dealings with Ukraine. The 72-year-old former Republican presidential nominee tweeted that "the President's brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling."

Those actions, however, had the effect of isolating Romney from his fellow Senate Republicans and from GOP voters in his own state, many of whom told NBC News last month that they strongly disapproved of his digs at the president and his passive reception of the House impeachment inquiry.

Collins, meanwhile, faces even a potential stronger backlash from Maine voters, because she's up for re-election next year.

A top target of Democrats in 2020 as they try to flip the GOP-controlled Senate, Collins last month called Trump’s public request for China to investigate Biden "completely inappropriate" but has noted she won't take a position on impeachment because she might be asked to serve as essentially a juror during a possible trial in the Senate. Public hearings in the House's inquiry are set to begin next week, and if the chamber votes to impeach, a Senate trial could begin next month.

That position seems to have alienated many conservatives who want to see their lawmakers defend Trump from the impeachment inquiry: Her once sky-high favorability ratings have fallen.

Murkowski, however, seems likely to be able to avoid those kind of consequences, for the time being.

"She'll be able to do her homework, as she always does, remain cautious, follow the facts," said Meek, of the University of Alaska-Fairbanks. "When the time comes, (she'll) make a strategic decision about whether the alleged abuse of power is important enough for her to take on that she'll have a lot of national Republicans coming after her.

"That," Meek added, "hasn’t stopped her in the past."