WASHINGTON — Democrats have been obsessed with the year 2020 — for its promise of redemption, revenge and a return of power — ever since Donald Trump won the presidency in November 2016.

Now the election year has arrived. But after a midterm rebuke of Trump at the polls, the House's impeachment of him last month and a year of campaigning by the contenders for the party's nod to take him on, his opponents find themselves no closer to their goal of ousting him than they were when he was inaugurated a little less than three years ago.

And they're spotting him a big messaging advantage, because to the extent he can stay on topic, he can make the case for himself and against them while they are still trying to figure out what they're going to sell to voters.

With voting beginning in little more than a month, they are in danger of wasting valuable time as they struggle to pick a captain and a course, still uncertain whether to go modest and moderate or big and bold in making their case for a change in the Oval Office. Trump's approval rating has rebounded to 45 percent, according to Gallup, which is where it sat on Inauguration Day in 2017, and some polls show him leading or in close competition with top Democratic contenders in battleground states that are widely considered to be the keys to victory this year.

"As difficult as it is to hear, Trump is and will be a formidable 2020 opponent," said Chris Kofinis, a veteran strategist who has worked on Democratic presidential campaigns. "Regardless of the nominee, he's going to be tough to beat, arguably tougher than in 2016, because his base is rock solid and independents remain more split than we realize."

Of course, the official selection of a Democratic nominee won't happen until the party meets this summer for its convention in Milwaukee, but the sustained relative strength of four candidates — former Vice President Joe Biden, Sen. Bernie Sanders, I-Vt., Sen. Elizabeth Warren, D-Mass., and former South Bend, Indiana, Mayor Pete Buttigieg — has more party insiders contemplating the possibility that the battle could end in a floor fight for the nomination.

But even in the absence of a consensus standard-bearer, Democrats might be able to start making the case for their policies if they could agree on a direction, other than away from Trump. For now, they are unified primarily in their opposition to him, and he has proven to be the inelastic man of American politics, equally incapable of gaining or losing much support regardless of events, his public relations efforts or the attacks that come his way.

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The problem for Democrats, as it has been, is that the party is roughly divided into thirds: A little less than a third back the moderate Biden, who is essentially promising a return to calmer times and incremental change; a little more than a third support Sanders or Warren, who have been all but locked at the hip in arguing for massive systemic changes that would tax higher-income and wealthier Americans to create new benefits for everyone else; and a little more than a third support someone in the rest of the field.

Buttigieg, 37, the only one of the top four not in his 70s, has positioned himself as a next-generation politician somewhere between Biden and Warren who, like Biden, can appeal to swing voters.

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The value of swing voters lies at the heart of the Democratic divide. Sanders and Warren contend that the party must offer — and the country needs — bold changes to health care, financial and other systems. They argue that their prescriptions will bring enough new voters to the polls to win at the presidential level and to effect changes in Congress, while also attracting swing voters who are fed up with the Washington establishment. But many Democrats are wary that expensive programs and new taxes will turn off swing voters in key states and hand the election to Trump.

Maria Teresa Kumar, president of the nonpartisan group Voto Latino, said progressives should focus on registering potential voters, particularly among the overlapping cohorts of younger Americans and the 15 million Latino and Latina Americans who are eligible to vote but aren't registered.

"If you're selling Nikes, you identify where the largest market opportunity is for your shoe and you go there," she said, adding that "there's no reason to have pendulum elections" in which the goal is to win a narrow majority by shifting swing voters when so many potential voters are available to be mobilized.

The differences among the candidates have been on display in half a dozen debates and in countless televised forums and town hall meetings in the early states, as well as through their campaign websites and social media accounts.

Unlike in 2008, when the policy distinctions between Barack Obama and Hillary Clinton were minor or backward-looking — as in the case of Clinton's vote in the Senate to authorize the Iraq War — or in 2016, when Clinton was the clear front-runner throughout the primary, the divisions among the leading Democratic candidates are wide, deep and multi-directional, both in broad approaches and in specific prescriptions.

But to the extent that Democratic voters have been attuned to the battle, they seem comfortable letting it play out for a while.

Over the last year, a handful of candidates have risen and fallen: There was a period during the summer when Warren took off before she stumbled explaining how she would pay for her version of a "Medicare for All" plan. Buttigieg sprung from anonymity up to about 12 percent briefly in national polling averages before trailing off a bit.

But the two leaders stand essentially where they did a year ago. Biden is at 28.3 percent in the Real Clear Politics average of polls, and Sanders is at 19.1 percent. On Jan. 1, 2019, they were at 27 percent and 17 percent.

No one expects Democrats to pick a nominee before Iowans caucus Feb. 3, and a long process did not prevent them from winning the White House in 2008, when Obama beat Republican Sen. John McCain. But for a party that was shell-shocked in 2016, the level of anxiety will only rise over time.

Former Rep. Jack Kingston, R-Ga., said the longer the Democratic primary lasts, the better it is for Trump, especially as the four front-runners, as well as billionaires Michael Bloomberg and Tom Steyer and businessman Andrew Yang, spend money to differentiate themselves in a battle for convention delegates.

"It's likely the only way a candidate can emerge from this is to go negative," Kingston said, allowing Trump to raise and spend money for the general election while Democrats' cash "will all have to be spent on fellow Democrats."

And Trump will have a messaging advantage, wielding the ability to say both what he's against and what he's for, until Democrats at least find common ground on what they're promising.