Before President Trump pressed his Ukrainian counterpart to “look into” Joe Biden, he had turned ridiculing the former vice president into something of a presidential pastime.

He attacked Biden at the White House and at campaign rallies. He attacked Biden on Twitter and on Instagram. He attacked Biden in France and in Japan, during news conferences and official speeches, in phone calls and in interviews, on Air Force One and in the Rose Garden, during morning “executive time” and in late-night tweet storms.

The president’s fixation on Biden is now at the heart of a historic impeachment inquiry launched by Democrats, who accuse Trump of using the power and leverage of the U.S. government to pressure Ukraine into investigating his potential rival.

In a July phone call with Ukrainian President Volodymyr Zelensky, Trump seemed to push for Ukraine’s government to develop evidence against Biden and son Hunter, according to a rough transcript of the call released by the White House on Wednesday. Trump said during the call that he would get U.S. Attorney General William P. Barr to work with the Ukrainians to investigate the Bidens, which set off a whistleblower complaint and events that could culminate in an impeachment trial.

The reinvigorated impeachment push this week is already leading the president to further focus on Joe Biden, as Trump and his supporters seek to shift attention from potential White House misconduct to whether the former vice president abused his position to help Hunter when he served on the board of a Ukrainian gas company during the Obama administration, charges that have little grounding in fact.

On Wednesday, Trump said he was willing to release the whistleblower complaint against him so long as information was also released about Biden’s dealings with Ukraine and China.

“[I] also insist on transparency from Joe Biden and his son, Hunter, on the millions of dollars that have been quickly and easily taken out of Ukraine and China,” Trump said during a news conference at the United Nations in New York, without offering any evidence to back up this charge. “Millions of dollars. Millions and millions of dollars taken out very rapidly while he was vice president. I think they should have transparency for that.”

Trump’s advisers say the president has targeted Biden in recent months for several reasons: He has emerged as a front-runner in a crowded field of Democratic contenders, he has a long record in Washington that allows the president to position himself as an outsider and he has been leading Trump in polling in key swing states.

Campaign aides previously had been wary of singling out any of the Democratic presidential candidates, opting instead to lump the group of more than 20 contenders together under the banner of “socialism.”

That began to change early this summer, as Trump’s focus on Biden hardened and the president began taking aim at the former vice president more often and more energetically than any other candidate. Trump’s attacks intensified as internal and public polling showed Biden as the president’s most competitive challenger, with large leads in states such as Michigan, Wisconsin and Pennsylvania.

Although several top Democratic candidates have avoided Trump in an attempt to focus on their own visions for the country, Biden has framed his campaign as a wholesale rebuttal to Trump from the very start.

Biden has also targeted areas of the country Trump won in 2016 and has made proving to Democrats that he could win back states in the Upper Midwest a centerpiece of his campaign.

“For someone who claims to be a ‘dealmaker,’ Donald Trump has certainly given Joe Biden a lot of rent-free real estate in his own head,” said Andrew Bates, a Biden campaign spokesman, listing ways Trump has fixated on Biden, including stirring “an unprecedented crisis by pressuring a foreign country to foment a universally debunked conspiracy theory.”

When Biden formally joined the race in April — launched with a criticism of Trump’s response to racist violence in Charlottesville in 2017 — Trump greeted him with a tweet.

“Welcome to the race Sleepy Joe. I only hope you have the intelligence, long in doubt, to wage a successful primary campaign,” he wrote. “It will be nasty — you will be dealing with people who truly have some very sick & demented ideas. But if you make it, I will see you at the Starting Gate!”

In the months since, Trump has widened his attacks on Biden, criticizing him over China, trade, Iran, North Korea, his work with segregationists, his support for the 1994 crime bill and his mental acuity.

The attacks intensified after internal polling data that leaked from Trump’s campaign showed Biden ahead of Trump by significant margins in states such as Pennsylvania, Wisconsin and Florida.

Campaign officials confirmed the data but said the numbers were already outdated by the time they leaked in June.

Trump dismissed the polls as “fake,” but his focus on Biden has persisted.

White House officials have also increasingly found ways to criticize Biden, sometimes bringing up the former vice president unprompted to contrast his record with Trump’s.

Last week, Trump’s campaign released a video that edited together clips of Biden’s verbal gaffes and television pundits — and Democratic campaign rival Sen. Cory Booker (N.J.) — questioning the former vice president’s age and mental abilities.

“You just wonder . . . ,” Trump campaign manager Brad Parscale said on Twitter along with the video clip. Although some Republican strategists have warned that focusing so much on Biden this early in the campaign would only elevate him in a crowded field, Trump has followed his instincts to meddle in the Democratic primary and sought to tear down the leading candidates.

Some Trump aides said the president targets Biden because the former vice president is a visible force and an easy target.

“Biden is the front-runner, and with his 40-plus years in politics, there’s a lot of material,” said Kelly Sadler, a spokeswoman for America First Action, a pro-Trump super PAC.

Biden’s penchant for gaffes and his previous failed attempts at running for president also make him a ripe target for Trump, said Bryan Lanza, an adviser to Trump’s 2016 campaign and transition efforts.

“Biden’s an easy punching bag in presidential politics because he’s a three-time loser,” he said. “He’s got a long record. He was in office when the deterioration of the middle class began.”

The attempt to cast Biden as the ultimate insider within a corrupt system has continued as Trump has pushed for investigations into Biden’s dealings with Ukraine.

The president has sought to use the same playbook that he successfully employed in 2016 against Hillary Clinton, who Trump portrayed as a corrupt self-dealer who represented a broken Washington.

In a statement Wednesday, Parscale made the link explicit, accusing “the Bidens, the Clintons, and other career politicians” of abusing their power.

Just weeks after Biden officially entered the race, Trump’s personal attorney Rudolph W. Giuliani was attempting to contact top officials in the Ukrainian government to discuss investigating Biden. Giuliani had started to make the case publicly and to Trump that Biden had been involved in a corrupt scheme to help his son by forcing out Ukraine’s top prosecutor in 2016.

Trump has since sought to broadcast those charges to the wider public.

Hunter Biden served for nearly five years on the board of Burisma, Ukraine’s largest private gas company, whose owner came under scrutiny by Ukrainian prosecutors for possible abuse of power and unlawful enrichment. Hunter Biden was not accused of any wrongdoing in the investigation. As vice president, Joe Biden pressured Ukraine to fire the top prosecutor, Viktor Shokin, who Biden and other Western officials said was not sufficiently pursuing corruption cases. At the time, the investigation into Burisma was dormant, according to former Ukrainian and U.S. officials.

In the past, Biden’s campaign has relished the fights with Trump, contending that it elevates him in the Democratic field to showcase what a general election would look like.

“I understand the president’s been tweeting a lot about me this morning. I wonder why the hell he’s doing that,” Biden, practically giddy, said during his first trip to Iowa. “Yo yo, woah woah woah. Anyway. I’m going to be the object of his attention for a while, folks.”

For much of his career, Biden has been seen as a politician with strong bipartisan relationships, the one who was asked to eulogize his Republican colleagues at their funerals, the one who attempted to see the good in his political opponents. He has come under criticism from Democrats for failing to adjust to the more combative partisan warfare.

But now the full apparatus of the Republican Party is crashing down on him, attempting to reshape his reputation in the eyes of a country that Biden’s campaign says already knows him and likes him.

Although Trump and his allies have cast him over the past few months as a bumbling and stumbling old man — calling him “a dummy” or “the weakest mentally” — they are now trying to paint Biden as a corrupt figure who can’t control his own son.

Biden has been less personal in his characterizations of Trump but has pointed to him as a historically bad figure who is an “existential threat” to everything America stands for.

He grew more animated this week, saying Trump was asking a foreign government to investigate him because, “he knows I’ll beat him like a drum.”

“It is an affront to every single American and the founding values of our country,” Biden said in a statement Wednesday. “This is not a Republican issue or a Democratic issue. It is a national security issue. It is a test of our democratic values.”