For more than 20 years. Sen. Susan Collins (R-ME) has served the citizens of Maine in the U.S. Senate. For most of that time, she has enjoyed a hard-fought reputation as a moderate Republican who methodically builds bridges and consensus in an era of political polarization. To millions of political observers, she exemplified the best of post-partisan leadership, finding a "third way" through the static of ideological tribalism.

However, all of that has changed since the election of Donald Trump in 2016. Voters in Maine, particularly those who lean left, have run out of patience with Collins and her seeming refusal to stand up to Trump. That frustration peaked with the nomination of Brett Kavanaugh to the Supreme Court.

All of this was going through the mind of Erik Mercer, a social worker in Maine who unexpectedly found himself in the same airport terminal as Collins last week. What started as a civil conversation between a concerned voter and his elected representative has become a catalyst for what may ultimately bring down her hopes for re-election in a very competitive 2020 campaign.

"It is our job to make our leaders accountable," Mercer told GOOD in a phone interview. "And if that means making them uncomfortable, then that is our responsibility." Still, Mercer said it was far from easy to approach Collins directly with his concerns. "I was nervous. I kept listing reasons in my head of why I shouldn't go talk to her," he said. "But as I watched her talking on the phone I couldn't help but wonder, 'What vital decision is she discussing right now?'"

Mercer says he approached Collins and asked if they could chat, a request she readily agreed to. However, when he pressed her on issues like supporting Kavanaugh, whether she backed the impeachment of Trump and a bevy of other issues, Mercer says Collins stonewalled him, refusing to take a position or answer for her voting record.

After their conversation stalled, the two "agreed to disagree" and went about their ways. However, Mercer says he then overheard Collins on the jet-bridge saying how "rude" he was in their exchange.

Later, as fate would have it, they ended up sitting just one row apart on their plane.

"As people walked [down the plane aisle] several of them said to me that they appreciated what I said to her," Mercer said. However, Collins could hear the interactions he was having from her seat and clearly wasn't happy about it. "I said to one woman who approached me, why don't you tell her yourself? And she said to me, 'I can't do it, I'm afraid I'll just get too angry.' There are so many people like her in Maine right now."

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Afterward, Mercer says he couldn't stop thinking about their interaction and how bothered Collins seemed to be by simply having to address a voter from the state she represents. "I've been thinking, if she's bothered by my tone, then where's her outrage over the president?"

So, Mercer took out a full-page ad in the Portland Press Herald in which he recounted their conversation and called on leaders like Collins to do a better job of listening to their constituents:

The letter has since gone viral across social media.

"The response has been overwhelming," Mercer said. "I expected it would make a little bit of a splash in Maine. But I'm hearing from people all over the country. It's really touching. A lot of elderly people around the country are reaching out to me and saying, I want to help you pay for this op-ed."

The outpouring of support has inspired Mercer to launch a GoFundMe campaign, "Make Susan Collins Listen to Maine," to raise enough money to publish another op-ed in the Maine Sunday Telegram. On his campaign page, Mercer writes:

"I'm raising money to pay for a full-page ad in the Maine Sunday Telegram, asking Senator Collins to start listening to average Mainers and not just the big money donors who support her. I've paid for one ad by putting it on my credit card, but I'm asking for your help to keep it going."

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When I asked Mercer how he thinks Collins has changed in recent years, he said he doesn't think she's actually changed that much. Rather, it's her refusal to adapt to, and confront, the Trump Administration's record that has made her unacceptable to independent but progressive-leaning voters in Maine.

"We are in a national crisis. What is happening in this country and the administration is not normal. Susan Collins is acting like it's normal," he said.

And even more than that, for him it ultimately comes down to what he sees as her unwillingness to be accountable to those people in Maine.

"She has not held a town hall in more than 20 years," he said. "She's provided no forum for her constituents to talk to her. She's not interested in us. And if she is interested in us, then answer my questions. I don't want this to become about me but going forward it's about all of us."

Mercer says he's intrigued by the idea of taking his op-ed model to other districts and states around the country where voters feel their elected leaders are not engaging directly with their voters. "Why can't we do this in Iowa next?" he said.