President Biden returned to Washington from his European trip, facing what could be the defining weeks of his first year in office. After a fast and relatively successful start during his first 100 days, he now confronts some of his biggest decisions in the second 100.

Three major issues are on the agenda in the weeks ahead: the pandemic, infrastructure and voting rights. Together they will reveal more about the president’s leadership skills, the nation’s seemingly intractable political divisions and whether bipartisanship is possible or even advisable.

Biden highlighted the first of these issues Friday when he spoke about the progress to date in vaccinating the population against the coronavirus — and the distance still to travel. Today, more than 175 million Americans have received at least one shot, and 300 million shots have been administered in Biden’s first 150 days, according to the White House. Cases, hospitalizations and deaths have declined dramatically.

That represents genuine progress. But the rate of daily vaccinations has slowed considerably from its peak earlier this spring, and the administration remains short of its current goal, which is to have 70 percent of adults receiving at least one shot by July 4.

According to the White House, about 65 percent of adults have received at least one shot, and about 55 percent are fully vaccinated. Fifteen states and the District of Columbia have reached that 70 percent target, the White House says, but many are far from it. Meanwhile, the spread of the delta variant, a more transmissible form of the virus that first arose in India, makes it more urgent to meet and even exceed the 70 percent goal as soon as possible and ultimately to get as many people as possible fully vaccinated.

The administration continues to grapple with demographic disparities in the distribution of vaccinations. Groups that have suffered disproportionately in numbers of cases and deaths — particularly Blacks and Hispanics — are being vaccinated at slower rates than Whites.

The Kaiser Family Foundation’s analysis across 40 states that report racial and ethnic characteristics of those who have received vaccinations shows that the percentage of Whites who have received at least one shot is 1.4 times higher than for Blacks and 1.2 times higher than for Hispanics. On a positive note, Biden reported Friday that 54 percent of vaccinations in the past month have gone to people of color.

Hesitation and skepticism toward vaccinations among many Black Americans have been an understandable reality from the start, given the sad history of their experience with the federal government and medical experimentation. The administration is focused on overcoming those deficits, but the gaps remain.

Politics is the other obstacle to Biden’s hopes of reaching or exceeding the 70 percent target. In public opinion polls, Republicans have consistently shown greater opposition to getting vaccinated than Democrats. State-by-state statistics bear this out. Every state at or near the 70 percent threshold as of this past week voted for Biden in 2020. The states with the lowest percentage of adults who have received at least one shot are those that backed former president Donald Trump.

The pace and pattern of vaccinations suggests that, as in so many other ways, America is and will remain as two nations, one overwhelmingly vaccinated and the other potentially far short of that. On vaccinations, as with mask-wearing during the worst of the pandemic, the unity that Biden talked about in his inaugural address has proved to be elusive.

The second issue facing Biden is the fate of his American Jobs Plan, the huge stimulus package that includes traditional and nontraditional infrastructure spending. Negotiations have dragged on, but there is some reason to think that Biden may be successful — if he is deft in his approach with Republicans and if he can persuade liberal Democrats to coalesce around a bipartisan compromise with the promise of more later.

The president’s first effort at finding common ground with Republicans failed: His negotiations with Sen. Shelley Moore Capito (R-W.Va.) collapsed, with Biden pulling the plug just before he left for Europe. A bipartisan group of senators has since agreed on a different plan; valued at nearly $1 trillion, less than half of what Biden originally proposed, and with differences over how the package would be funded.

One big question is whether a bipartisan package can get the necessary 60 votes in the Senate. Currently 11 Republicans have indicated support for the proposal as it now stands. Biden would still need all 50 Democrats to go along. Liberal Democrats in Congress, and their outside allies, are grumbling about the limitations they see in the compromise proposal and are restless at the pace of negotiations, saying it is time to act.

The question the liberals face is: Would they really sink a bipartisan deal negotiated by the president, especially if they have the option to advance a second package under the terms of reconciliation, which would require a simple majority to pass?

However, a bipartisan bill of more limited scope might be the price Biden and liberals must pay to get support from Sen. Joe Manchin III (D-W.Va.) and some other moderates on a second package.

Biden has made clear his desire to reach accommodation with Republicans to fulfill his pledge to govern in a bipartisan fashion. But he does not have unlimited time to decide whether to take what’s available, given the time that would be needed to get a second package done under reconciliation.

Sen. Bernie Sanders (I-Vt.), who chairs the Senate Budget Committee, is working up a package valued at $6 trillion, which means both trains are moving on the track. The real issue is how Biden sizes up the risks and rewards and whether he can satisfy both his desire for a bipartisan compromise and his ambitions to deal expansively with domestic challenges.

Before anything definitive happens on infrastructure, the Senate will confront the most contentious issue on the summer calendar when the For the People bill comes to the floor in the days ahead. The massive bill would establish regulations for conducting federal elections in the states (early voting periods, mail ballots, automatic voter registration, etc.); attack the issue of gerrymandering; and provide for public financing of elections under certain circumstances.

For Democrats, the legislation is a counter to Republican-led efforts in state legislatures to pass measures that would restrict voting access. Biden has been highly critical of the GOP-backed voting legislation in the states, calling some of the laws “Jim Crow 2.0.”

The national voting rights bill passed the House earlier this year but appears to have no chance of passing the Senate, given the opposition of Minority Leader Mitch McConnell (R-Ky.) and his GOP colleagues. Many Democrats, who see national voting regulations as critically important, have proposed changing or eliminating the filibuster to overcome solid Republican opposition, but Manchin has said he would not support any changes in those rules.

This past week, Manchin came forward, unexpectedly, with a compromise proposal. Among the list of ideas, Manchin’s plan would make Election Day a federal holiday, provide for automatic voter registration, mandate 15 consecutive days of early voting for federal elections, ban partisan gerrymandering and require a form of identification for all voters.

The proposal doesn’t go as far as many liberal Democrats would like, but it is more than many Democrats might have anticipated from Manchin and has affected the dynamic of the discussion. The proposal drew praise from Stacey Abrams of Georgia, who has been in the forefront of the battles over voter access, but McConnell said he opposes it. Will McConnell’s immediate dismissal of the Manchin plan affect how the West Virginia moderate thinks about whether Republicans are serious about working with Biden?

The Senate’s consideration of the For the People bill will be one step, but not the definitive moment, in the intense national debate over strengthening democracy and protecting voting rights throughout the country. But it presents Biden with one more challenge in a summer filled with them.