At counter-WHCD rally in Wisconsin, Trump rips Democrats' ‘collusion delusion,’ takes aim at 2020 presidential field The president skipped the annual D.C. gathering for the third straight year.

At his first campaign rally since the release of special counsel Robert Mueller's report on Russian interference in the 2016 election, President Donald Trump decried what he called the "collusion delusion," and took aim at the crowded field of 2020 Democratic candidates as his battle to win a second term in the White House continues to intensify by the day.

"Liberal democrats put all their hopes behind their collusion delusion, which is totally exposed as a complete and total fraud," Trump said in a nearly two-hour long speech in front of roughly 10,000 supporters in Green Bay, Wisconsin, a swing state critical to his re-election hopes.

"Look at what's happened with the scum that's leaving the very top of government. People that others used to say oh that's...dirty. These were dirty cops. These were dirty players," Trump said in an apparent reference to Mueller and his investigators.

Trump called the special counsel's investigation "the greatest political hoax in American history," and called out potential Democratic rivals from former Vice President Joe Biden, or "Sleepy Joe," to Vermont Senator Bernie Sanders, or "Crazy Bernie," to Massachusetts Senator Elizabeth Warren, for whom the President revived his "Pocahontas," moniker.

The president eagerly labeled his opponents as socialists, saying "Democrats are now the party of high taxes, high crime, open borders, late-term abortion, hoaxes and delusions."

In a stem-winding speech that touched on a wide-range of policy issues, Trump also claimed that the administration is sending illegal immigrants to sanctuary cities, a controversial proposal that the administration originally claimed was just an idea under discussion, but now the president says it was actually his "sick idea."

"100,000 illegal immigrants arrived in our borders, placing a massive strain on communities and schools and hospitals and public resources like nobody's ever seen before. Now we're sending many of them to sanctuary cities," Trump claimed, "I'm proud to tell you that was my sick idea."

Earlier this month a White House official told ABC News the idea was "a suggestion that was floated and rejected, which ended any further discussion."

Trump also took another swipe at the late Sen. John McCain, a frequent target of his criticism even after his death, for his vote against the repeal of the Affordable Care Act.

"We should have had health care, but one man decided to vote against us at the last moment. I was — even though he campaigned for eight years repeal and replace, but that's okay." Trump sad.

Trump added that he and the Republicans would be revealing a new healthcare plan after the 2020 election, but declined to offer any additional details on the plan.

"We're coming up with a great package of healthcare. We're going to be the party of healthcare. We're coming up with a great package, after the election, we got to take back the House," Trump said.

The president also swiped at "Empire" actor Jussie Smollett, calling him a "third rate actor" and the situation regarding his arrest and release a "disgrace to our nation."

Trump also complained about the amount of money the United States is paying to protect "rich countries," like Saudi Arabia militarily.

"I called the King, I like the King I said we're losing our a-- defending you and you have a lot of money," Trump said.

Trump's victory in Wisconsin in 2016 marked the first time a Republican presidential candidate won the state since the mid-1980s, and will be hotly contested in 2020 as Democrats aim to re-build the so-called "blue wall" of Midwestern states that helped propel the likes of Barack Obama and Bill Clinton to victory in their presidential bids.

However, 2018 was a banner year for Democrats in Wisconsin, when the party swept all statewide elections and unseated Republican Gov. Scott Walker, who was seeking a third term in office but was defeated by Democrat Tony Evers.

The victories in Wisconsin and Michigan, where Democrats flipped the governor's mansion and two congressional seats, underscore the importance of both states for Trump's re-election prospects — and the difficult political terrain he may encounter in 2020.

Saturday's rally was Trump's third campaign event this year.

The president has held re-election rallies so far in El Paso, Texas, and Grand Rapids, Michigan, as his campaign ramps up to take on whoever emerges from the field of crowded Democrats that swelled to 20 this week with the official entry of former Vice President Joe Biden.

The president's rally was also Trump's most sustained and direct response to Mueller's report, and the subpoenas from Democrats on Capitol Hill, which continue to loom over his presidency.

In the wake of Mueller's report, Trump has continued to rail against the special counsel's investigation, tweeting earlier this week that is was "'composed' by Trump Haters and Angry Democrats."

Ultimately, the special counsel's office did not find sufficient evidence to suggest that members of the Trump campaign or anyone associated with it conspired or coordinated with the Russians. The report made no conclusion, however, on the matter of possible obstruction of justice by the president.

Despite Mueller's detailed findings into Russian meddling, Trump's senior advisers maintain it was the candidate's message that ultimately resulted in his upset 2016 victory.

"Donald Trump won — we didn't need WikiLeaks. We had Wisconsin. He won because he was the better candidate with a better message," Kellyanne Conway, counselor to the president, told ABC News' George Stephanopoulos on "This Week" last Sunday.

During the rally, the president also invited on stage White House press secretary Sarah Sanders who seemed to relish the crowd's chants of her name and acknowledged that last year she was at "a slightly different event" where she didn't get "the best welcome." Last year, Sanders bore the brunt of comedienne Michelle Wolf’s acerbic routine at the the White House Correspondents' Dinner.

Trump's rally coincided with this year's press dinner, which he skipped for the third year in a row, and his administration boycotted the celebration of journalistic freedoms.

During the dinner, keynote speaker, presidential biographer and historian Ron Chernow gave a historical, and, at times comical, account of the sometimes tense relationship between presidents and the press since the nation's founding and the need to hold governments accountable.

“My main theme tonight is that the relations between presidents and the press are inevitably tough, almost always adversarial, but they do not need to be steeped in venom,” Chernow said.

He also lauded the journalistic tradition of exposing the ills of slavery, discrimination, labor abuses and government corruption.

The historian advised journalists on how to respond to President Trump when he dubs the press the "enemy of the people" advising journalists to take inspiration from Noreweigan playwright Henrik Ibsen's play about a man who was shunned for telling an unpopular truth, "An Enemy of the People."

"I hadn't realized that the president was a student of Norwegian literature, did you realize that?” Chernow joked and told the crowd to wear the title as a badge of honor.

ABC News' Kelsey Walsh contributed to this report.