This president towers over the 2020 Democratic presidential primary.

No, not President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE.

I’m talking about President Obama.

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Obama left office with a 59 percent approval rating and a 37 percent disapproval rating, according to Gallup.

In late January, the Gallup poll ratings for President Trump were the exact inverse of Obama’s numbers — 59 percent disapproval and 37 percent approval.

A July 2018 poll from the Pew Research Center found 31 percent of Americans rank Obama as the best president of their lifetimes. In fact, close to half of Americans, 44 percent, said Obama is either the best or the second-best president they’ve known.

As Democrats begin their campaign for the party’s 2020 nomination, Obama is the party’s unrivaled powerbroker.

He will be the biggest speaker at the party’s 2020 convention.

His wife, Michelle Obama Michelle LeVaughn Robinson ObamaMichelle Obama: 'Don't listen to people who will say that somehow voting is rigged' Michelle Obama and Jennifer Lopez exchange Ginsburg memories Social media platforms put muscle into National Voter Registration Day MORE, might be the second biggest.

Her book, “Becoming,” has been the best-selling book in the country for the last three months. If she ran for her party’s nomination, it would be hard to stop her. Even the Trump-friendly Rasmussen poll shows her beating the current president in a general election.

And don’t forget, President Obama has his own book coming out on his time in the White House. It will likely be published in the heat of the 2020 campaign. He will have a huge national platform and every reason to finally drop all restraint and take on Trump.

Just seeing him again will boost Democrats. He provides a striking contrast to Trump’s era of alleged pay-offs to porn stars, chaos at the White House and allegations of collusion.

In a Democratic primary that will almost certainly have more than a dozen candidates, being anointed by Obama — if he makes an endorsement — will be rocket fuel for one lucky candidate.

How times change.

Obama was not always the far left’s hero.

They used to complain that the first black president so feared being defined as a black radical that he moderated liberal policies and muted his responses to GOP obstruction.

Now, with Trump as president, those same liberal voices are raised to defend Obama’s record.

Trump set them off by attacking Obama’s policies while taking credit for the results.

The strong economy and low unemployment rate?

They are largely a continuation of Obama’s successful economic policies, which brought the country back from the Great Recession.

As the Washington Post noted late last year, the economy “added more jobs in every year of Obama’s second term than it did in Trump’s first year.”

Going after ISIS and other Islamic terrorists?

Obama had degraded them with drones and special forces before Trump became president.

And what about Trump’s attack on ObamaCare, while failing to produce a better plan?

Congressional Democrats are in charge of the House of Representatives because they campaigned in the midterms as fans of ObamaCare and its protections for people with pre-existing conditions.

Every one of the 2020 Democratic presidential candidates is defending the Affordable Care Act, while several call for “Medicare for All.”

It is hard to name a Democrat running for the nomination who is not part of the Obama legacy.

Former Vice President Biden is the leading candidate for the nomination because of his eight years as Obama’s deputy.

Sen. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE’s (D-Calif.) success as a prosecutor led the late journalist Gwen Ifill to describe her as “the female Barack Obama Barack Hussein ObamaMichelle Obama and Jennifer Lopez exchange Ginsburg memories Pence defends Trump's 'obligation' to nominate new Supreme Court justice The militia menace MORE.” Now she is following in his footsteps as a first-term senator running for the White House.

Julian Castro became a national political figure when Obama tapped him to give the keynote address at the 2012 Democratic National Convention. Obama later named him as his second-term secretary of the Department of Housing and Urban Development.

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Sen. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.) was an academic when Obama named her to oversee the federal government’s response to the 2008 global financial meltdown. Later, she worked with congressional Democrats to create the Consumer Financial Protection Bureau.

Sen. Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (D-N.J.), another Obama ally, is constantly compared to the 44th president.

The upcoming campaign is turning into a struggle between the political poles represented by Obama and Trump.

On one side is Trump’s appeal to fear and grievance — on immigration, for example. On the other side, the Democrats are returning to Obama’s hallmarks of hope and change — for example, creating a better health care system.

In his farewell address, Obama rolled out his party’s answer to Trump:

“If you are tired of arguing with strangers on the internet, try talking with one of them in real life,” Obama said. “If you are disappointed by your elected officials, grab a clipboard, get some signatures, and run for office yourself. Show up. Dive in. Stay at it.”

For every Democrat, the bottom line to winning the nomination is convincing fellow Democrats they know how to beat Trump.

But first they have to convince Obama.

Juan Williams is an author, and a political analyst for Fox News Channel.