WASHINGTON — With full control of the White House and Congress for the first time in a decade, Democrats are wrestling with how to use that power: Seek out Republican support in the name of bipartisanship, or swing for the fences.

Sen. Bob Casey wants home runs.

“I’m in the camp of go big or go home,” the Pennsylvania Democrat said in an interview last week, before quickly adding a note of old-fashioned caution. “Maybe the ‘go home’ is a little harsh.”

Casey, once positioned as a deliberate moderate, wants Democrats to push hard in the early days of President Joe Biden’s administration, arguing that GOP support is unlikely and the needs of the moment are dire.

“You have all these challenges ahead of us and I don’t think we have any choice but to be proposing bold and transformative change,” Casey said, pointing to the health and economic crises stemming from the coronavirus, the threat of climate change, and racial inequality. “We just have so many things we’ve got to get done and majorities can be fleeting. They can evaporate in two years.”

Casey, 60, said that he hopes solutions can be bipartisan but that he would support moving ahead without the GOP by using reconciliation — a Senate procedure that allows some bills to pass with a bare majority. Democrats could vote to begin that process as early as this week.

And he’s “open” to eliminating the filibuster, the rule that requires most legislation to secure 60 votes out of 100, despite taking the opposite position in 2017, when President Donald Trump and Republicans held the levers of power. Casey signed a bipartisan letter that year urging against ending the filibuster.

» READ MORE: Bob Casey says he’s open to killing the filibuster and advancing Biden’s agenda without GOP support

Casey’s aggressive posture mirrors the hard-charging approach from many Democrats who see a rare window of opportunity and are thirsty for big proposals after years of seeing their ideas stalled by the GOP.

It also matches Casey’s personal evolution from a centrist Democrat who opposed tougher gun laws and same-sex marriage to one who reversed his views on both issues and has adopted more liberal positions and a more combative tone.

The senator, a rare Democrat who personally opposes abortion, has boasted about maintaining funding for Planned Parenthood. He railed against Trump, announcing that he would oppose any Supreme Court nominee in 2018 before the president even named one (it wound up being Justice Brett Kavanaugh). And last year Casey was one of just 23 senators to vote for a plan by Sen. Bernie Sanders (I., Vt.) to cut defense spending by 10%.

In 2017, some liberals dubbed him “Woke Bob Casey.” They were only half-joking.

Since first being elected in 2006, “Bob Casey has certainly gravitated further and further left, and I would argue is almost unrecognizable ideologically from the Bob Casey who was [first] elected,” said John Brabender, a Republican strategist who worked for Sen. Rick Santorum, the incumbent Casey defeated that year.

Casey’s leftward progression isn’t new — it has unfolded over nearly a decade, starting with a shift on guns after the Sandy Hook school shooting in 2012. Until now, however, few of Casey’s policy changes have resulted in action, since most have come amid divided government or Republican control in Washington. And they didn’t hurt him politically (and maybe helped) in 2018, when the senator was overwhelmingly reelected.

Now, however, Casey is part of a razor-thin Democratic majority, and a close friend and fellow Scranton native is in the White House, offering a chance to make some of his ideas into reality — and a test of how far he’s willing to push.

“We’re going to find out exactly what type of Democrat Bob Casey is today,” Brabender said.

Even though Casey isn’t up for reelection until 2024, Democrats’ hold on power, and Biden’s leverage, will be on the line in the 2022 midterm elections, when voters will have their say on whether the new majority deserves to retain control.

Casey said he’s approaching the next two years carrying lessons from the last time Democrats had total control, when President Barack Obama took office facing another crisis in 2009. He argued that Democrats made a mistake by trying to scale back their proposals for economic stimulus and health care in a mostly futile effort to draw Republican support. In the end, their bills were less ambitious and they still faced accusations of partisanship.

“I just don’t think we can repeat those mistakes,” Casey said. “We need bold, robust legislation and maybe by definition that means it won’t be bipartisan.”

He argued that Biden and fellow Democrats should seek out GOP votes, but not linger if they don’t seem forthcoming. Even though Casey joined the Senate in 2007, this will be only the third year during Casey’s tenure in which his party holds the White House, Senate, and House.

His comments to The Inquirer were made before a group of 10 Republican senators wrote to Biden on Sunday, offering a relief package about one-third the size of what the president has proposed, pitching the plan “in the spirit of bipartisanship and unity.”

Republicans, who blocked much of Obama’s agenda after his first two years in office, argue that the aggressive push by Biden and Democrats undercuts the president’s mantra of unity. Most in the GOP see the $1.9 trillion coronavirus relief plan as too big and larded with bad policy, such as a $15 minimum wage, which Republicans argue will destroy jobs.

“If they wanted to find the common ground that we have between Democrats and Republicans, they could do that,” said Sen. Pat Toomey (R., Pa.), pointing to bipartisan deals over previous coronavirus relief packages. But if Democrats use reconciliation, “it’s clear that they’re done with that.”

Casey, hitting back at the GOP in general (though not Toomey specifically), said: “These are the same people who either applauded or stood back when the president was signing the Muslim ban. There couldn’t have been more efforts to divide and pull the country apart.”

Republicans also used reconciliation to unilaterally advance their major legislative efforts under Trump, including his signature tax cuts.

» READ MORE: Pat Toomey is ready to work with Joe Biden. A little.

While Casey’s evolution — on substance and tone — is notable for him, it has largely kept him inside the Democrats’ increasingly liberal mainstream.

“He’s never gone against the grain,” said Mark Dion, a Republican consultant who has worked on Pennsylvania campaigns. “He may move further left on the issue, but he’s not going to be the one out there waving the flag.”

Democrats are fairly united around the broad scope of their coronavirus plan, but fissures between the party’s left and center could emerge on issues such as climate change and other topics. Those debates could challenge Casey if he’s forced to choose between paths in a 50-50 Senate where Democrats can’t afford any defections (Vice President Kamala Harris can cast tie-breaking votes).

Several people close to Casey predicted he will likely look for the consensus position and usually land wherever Biden does.

“Both of them, Biden and Casey, are practical,” said Jim Brown, Casey’s former chief of staff. ”A lot of their priorities would just naturally be parallel.”

They also have a long and deep connection. “The Bidens and the Caseys, that’s a multigenerational relationship,” Brown said.

The families aren’t just both from Scranton — they’re also from the same street. Biden was close with the senator’s father, Bob Casey Sr., when the elder Casey was governor of Pennsylvania and Biden was dubbed the state’s “third senator.”

And when the younger Casey arrived in the Senate, Biden, then chair of the Foreign Relations Committee, pushed party leaders to put Casey on the panel, as well, becoming a mentor, Brown said.

So when Biden launched his presidential campaign with a 6 a.m. tweet in 2019, Casey endorsed him at 6:37. When Biden formally accepted the Democratic nomination for president, Casey stood outside Biden’s childhood home in Scranton to announce Pennsylvania’s vote tally. And as Pennsylvania’s vote count dragged on after Election Day, Casey repeatedly took to Twitter with videos explaining why he was sure Biden would win, with a map of the state as his backdrop.

Casey said he expects to have disagreements with Biden at times, though he couldn’t name one that has come up yet.

» READ MORE: The Divided States of Pennsylvania: How one state embodies America’s political discord

Even as he voices support for more liberal efforts, the bills Casey personally writes rarely ruffle feathers, or grab big headlines.

He has worked to carve out a niche on children’s issues and named his personal focus, outside of the big-ticket bills, as “kids, jobs, and seniors.” His top personal legislative priority is a measure to significantly expand the tax credit for child care, arguing it’s even more urgent now that many people are struggling to return to the workforce. A version of his proposal is included in the Biden coronavirus package.

With opportunity at hand in the Senate, Casey said he has no intention of running for governor in 2022.

“I have this job at least for four years, that I’m aware of,” he said.