(CNN) Editor's note: This story -- originally published on April 14 -- has been updated to reflect Biden's entry into the 2020 presidential race.

Delaware Democrat Chris Coons has fewer friends at work than he used to.

Throughout his Senate career, Coons has been known for working across the aisle and forging tight relationships with high-profile Republicans who shared common interests — but with several of his closest allies now gone, that job has gotten harder.

Coons is known for drafting bills that can get GOP support. And when a Republican introduces a bipartisan bill, it's often because his name is on it.

He's still working with Republicans — he introduced legislation this year with Texas Sen. Ted Cruz on Cambodian trade, and he paired up with Oklahoma Republican James Lankford to bring forward a bill to require an exclusion process for the Trump administration's tariffs on Chinese goods.

He's also found a partner in freshman Utah Republican Mitt Romney, who cosponsored a bill alongside Coons and Virginia Democrat Tim Kaine earlier this month to enhance America's security and analysis practices related to threats posed by China.

"I am constantly looking for an opening," Coons told CNN in an interview. "If I can find something to do with Ted Cruz, I can find something to do with everybody. And at the end of the day, that's the only way this place has any hope of survival, because at this point we are blues and reds, shirts and skins, barely speaking to each other on everything."

Yet, though he's busy reaching across the aisle on Capitol Hill, Coons has already chosen sides in the 2020 presidential race, backing his fellow Delaware Democrat Joe Biden. "I've said over and over I'm optimistic he will run. I'm now confident he will run, and I look forward to campaigning with him and supporting him," he told CNN in early April. Biden announced his candidacy on Thursday.

Polarization has gone up since the midterms

In the last Congress, Republicans had a slim majority of just 51 votes in the Senate, giving Democrats more power to influence or block bills if just a couple Republicans chose to split with GOP leaders. Republicans won more seats during the 2018 midterms, now holding an increased majority of 53 seats.

Gone from that number, though, are some of Coons' closest GOP allies.

Former Arizona Sen. Jeff Flake , who bonded with Coons over their travels in Africa, is now a CBS commentator. Tennessee Republican Bob Corker, who worked with Coons often, also called it quits last year. And the late Arizona Sen. John McCain passed away from brain cancer last year. He was close with Coons — the two traveled together and collaborated on tough issues, such as immigration. Fittingly, Coons recently took over McCain's old Senate office.

Coons' friendships have given him influence in the past. He played a critical role during the Senate's high-profile consideration of Supreme Court nominee Brett Kavanaugh, convincing Flake to ask GOP leaders for an FBI investigation into sexual assault allegations against the nominee. It delayed the vote by a week, and raised the possibility that Flake, a key swing vote, could oppose Trump's pick.

Perhaps the best-known instance of Coons' uncommon penchant for bipartisan courtesy came last spring: the senator's close friend Georgia Republican Sen. Johnny Isakson was absent to attend a funeral, causing the Senate Foreign Relations Committee to become deadlocked over Secretary of State Mike Pompeo's nomination. Coons, who opposed Pompeo, agreed to use the old Senate tradition of "pairing" votes to effectively break the tie to allow the nomination to proceed to the Senate floor.

"I love the guy," Utah Republican Mike Lee told CNN. "I think he's fantastic even though he and I frequently disagree. I always have found him to be someone who can disagree without being disagreeable."

Building friendships through prayer

Coons has built many of his friendships through the Senate prayer breakfast, a weekly gathering of lawmakers from both parties who sing hymns, pray, and discuss their personal lives and struggles. Coons and Oklahoma Republican James Lankford co-lead the group and are responsible for organizing the National Prayer Breakfast, which takes place on the first Thursday in February every year.

Coons speaks about his faith often. He not only attended Yale law school, but also earned a master's degree from its divinity school.

"He's very passionate about his faith. It's very, very personal to him and it shows, and he's not afraid to talk about that," Lankford told CNN in an interview. "He's comfortable enough in his faith to be able to talk about it personally and to be able to say at times, 'It's a tough decision. I'm going to pray that through.' And that's pretty rare around this place."

Coons' theology plays a major role in his approach to Congress and the relationships he has forged with Republicans.

"That perspective says not, 'I'm righteous and you aren't,' but we're all fallen and all of us are desperately in need of forgiveness," Coons said of Christianity. "It makes it possible for me to see my colleagues not as horrible, evil, broken people who are trying to do terrible things, but as people I vigorously disagree with ... They're people. They're just trying."

He added that because of his faith, he strives to be self-critical rather than self-righteous — "I represent 900,000 people. Any one day, 45% of them think I'm wrong," he said. "Therein should lie some humility."

But maintaining cross-party relationships has become even more challenging during Trump's first two years in office, as Republicans in Congress have increasingly united behind the president.

"It can be hard because the President is very demanding and doesn't hesitate to put Republicans in very awkward positions, and that can run into conflict with long held positions and it can run into conflict with bipartisan agreements that are in the works," Rhode Island Democratic Sen. Sheldon Whitehouse told CNN. "People like Chris on our side and a number of members on the Republican side row against that tide."

Pressure from the left

The former New Castle county executive was first elected to the Senate in a 2010 special election to fill Joe Biden's seat, and was elected to a full term in 2014. He faces re-election in 2020, but in a safe Democratic state. He's not exactly under pressure to act as a centrist or cooperate with Republicans, like West Virginia's Joe Manchin — he does it because he wants to.

"I'm a legislator. There's people here who apparently aren't interested in legislating," Coons said when asked about the Green New Deal and other sweeping ideas from freshman House Democrats. "There is a role for people who are really ambitious and want to transform our society and our economy. But that often doesn't extend to actually legislating."

Many of the party's most aspirational goals are being championed by 2020 presidential hopefuls. But Coons hasn't joined in on the party's leftward lurch, even as his colleagues have embraced proposals such as Medicare for All, Sen. Elizabeth Warren's wealth tax, and Sen. Bernie Sanders' bill to eliminate tuition and fees for community college students and for lower and middle income students at four-year schools.

Coons has instead introduced centrist plans for similar issues — bills he says are more likely to get signed into law. He recently brought forward legislation to help pay college tuition for Americans who volunteer in national service programs, as well as a retirement savings bill that would establish a minimum contribution requirement for employee savings plans.

That divide may become more apparent when Coons comes up for re-election. He has already faced heat from the progressive grassroots for his emphasis on working with Republicans, and he expects the backlash to increase as the election cycle kicks into gear.

Brian Fallon, a former Hillary Clinton aide who now leads the progressive advocacy group Demand Justice, has been a vocal critic of Coons, suggesting last year that Democrats would be better off if his Republican opponent had won instead. And leading activists, such as Sean McElwee of Data for Progress, a think tank that advocates for ideas like the Green New Deal and abolishing Immigration and Customs Enforcement, contend Coons' tactics haven't been effective enough because he hasn't been able to persuade Republicans to sign onto bold progressive policies.

"Delaware is a pretty blue state," McElwee told CNN, arguing Democrats are "wasting a safe Senate seat on a guy who wants to do bipartisanship."

Coons shrugged off the criticism.

"I do think that I will get some challenge," he said of a potential primary opponent. "They don't scare me. It's democracy, yay, come on in."