CNN  — 

With confidence and elan, President Joe Biden rallied allies abroad last week around the viability of 21st century democracy. Proving it here at home will be harder.

Members of the transatlantic coalition – at meetings of the Group of Seven, the North Atlantic Treaty Organization and the European Union – expressed exuberant relief during the new president’s first overseas trip. Biden’s predecessor, Donald Trump, had undermined their shared objectives while showing subservience to the Russian autocrat Biden confronted on his last stop.

But Biden has staked his case on the domestic success of his own presidency. And that poses an excruciating challenge in two overlapping ways.

The first is achieving his legislative agenda. To follow his top initial priority of Covid relief, Biden has elevated a massive proposal for spending on physical infrastructure and providing help for struggling families to climb the economic ladder.

He chose it for the popularity of its elements and the effects he envisions in expanding opportunity and changing the trajectory of America’s economy. Its enactment represents the quintessential test of his vow to show that democracies can “deliver for their people.”

Yet ultra-thin Democratic congressional majorities leave prospects for overcoming Republican resistance in doubt.

During Biden’s trip, developments on Capitol Hill gave the White House a glimmer of hope. Ten senators from each party edged toward a bipartisan compromise on physical infrastructure elements of his plan.

Passage of that compromise could in turn reduce the price tag of – and increase the willingness of moderate Democrats to vote for – a follow-on package with the remaining elements through a budget “reconciliation” process requiring only Democratic votes. If Republicans block the compromise, moderate Democrats will see party unity on a reconciliation package as the only route to action.

“Progress but still a lot of bumps ahead,” a senior administration official told CNN. So long as 41 of 50 Republican senators can kill one part by filibuster and one of 50 Democrats can kill the other part by defection, it’s safest to bet on the bumps.

Biden’s second huge challenge is maintaining control of government for his party over a GOP displaying increasing overtones of authoritarianism. Upping the ante on Senate Minority Leader Mitch McConnell’s famous though fruitless pledge to make Barack Obama a one-term president, GOP Wyoming Sen. John Barrasso has publicly said he aims to hold Biden to a “half-term” of effective governance.

The long-established pattern of midterm elections points toward Republicans pulling that off. The typical midterm gain for the party not holding the White House would easily erase the Democrats’ 222-212 House majority; a mere one-seat Senate gain would make McConnell majority leader again.

Moreover, Republicans are using red-state governments to tilt the odds in the wake of Trump’s election lies and the failed January 6 insurrection at the US Capitol. Their efforts include tightening partisan control of election-result certifications and curbing 2020 voting practices.

Democrats have sounded alarms about voting restrictions. But the familiar decennial process of redrawing House district boundaries poses a larger threat to their majority.

“The upcoming fights over redistricting are going to make debates over changes to voting laws look like a walk in the park,” said David Wasserman, an expert on redistricting at the Cook Political Report. With Republicans in full control of state governments drawing 187 districts to the Democrats’ 75, gerrymandering alone could flip the House.

Biden found a glimmer of hope last week for the Democratic effort to safeguard voting rights, too. The most recalcitrant Democratic senator, Joe Manchin of West Virginia, unveiled what he billed as a bipartisan compromise accepting Republican calls to require voter identification while outlawing partisan gerrymanders, making Election Day a national holiday, and ensuring 15 consecutive days of early voting.

It won’t produce bipartisan comity. McConnell promised roadblock opposition after Black Georgia politician Stacey Abrams, a leading voting-rights activist, embraced it.

As with infrastructure, Democrats could still profit from Republican resistance to compromise on voting rights.

One possibility is that Manchin himself could join other Democrats in voting to sidestep filibuster rules to pass his plan in the name of protecting democracy. More likely, the specter of abuses of power by a GOP blocking an independent investigation of January 6 will offer Democrats a powerful 2022 mobilization tool.

Biden’s party has other assets. Having lost House seats in 2020, they hold fewer marginal seats to protect. Trump remains dominant inside the GOP but a political burden outside it. Turnout by his blue-collar base may sag without him on the ballot.

The reopened economy, boosted by Biden’s $1.9 trillion Covid relief package, is surging as the pandemic recedes. Biden has steadily held a net-positive job approval rating – just like Bill Clinton in 1998 and George W. Bush in 2002, the only two presidents in the last half-century to gain midterm seats.

Yet the historical ebb-tide Biden faces has been consistent and strong. His partisan opponents hold potent weapons and relentless determination to see him fail. Even for an experienced President with seasoned advisers, changing Vladimir Putin’s behavior may come to look easy by comparison.