Trump accuses Democrats of 'poisoning' democracy as they attack him during 2020 debate

President's Phoenix rally is first of three in as many days during West Coast swing

Donald Trump told supporters in Phoenix that Democrats led a "pathetic attempt" to "overthrow" his presidency and the entire federal government, mocking the opposition party as he kicks his reelection campaign into full gear.

The president accused Democrats of trying to "poison" American democracy – just as they accuse him of doing in an early preview of what promises to be a top attack line by the Republican president.

He said he has had to survive "very unfair witch hunts and partisan ... crusades" to take him down, before openly mocking Democrats.

"And guess what? They failed," he said to loud applause. "And our polls numbers today are higher than they've ever been before."

"I actually think we're going to win by a lot – just like we did last time," Mr Trump said to more applause.

Mr Trump's 2020 campaign slogan is "Keep America Great." But he appeared to contradict that when he said Democrats, with investigations and an impeachment inquiry, "really stole three years from us."

The president launched the rally by slamming "radical" Democrats, whom he called "socialists" and told the audience he plans to "be back" in the state "a lot" during the campaign. Arizona is on a list of states that could be in play come November; Mr Trump won it in 2016 by over 3 percentage points.

As he typically does at official White House and campaign events, he hailed the state of the economy and railed against previous presidents over trade deals, saying, "America is no longer for sale."

Mr Trump again acknowledged he "loves" political programming on television, and showed he is studying the Democratic primary and polling data. Former New York City Mayor Mike Bloomberg has been surging; for the second time in public remarks on Wednesday, the president referred to him as "Mini Mike," a shot at the former mayor's height. He also deemed Tom Steyer, who pushed for Mr Trump's impeachment long before House Democrats did just that, a "jerk."

"How'd that work out, Steyer? You jerk," Mr Trump said to laughter from the crowd.

And he hit Democrats and the Obama administration over HealthCare.gov, the website that accompanied the Affordable Care Act, claiming his 13-year-old son Barron Trump could have designed a better site for a couple of US dollars. The Democrats' site launched with a slew of problems, to the embarrassment of the Obama White House.

The elbow-throwing commander in chief also had some tough words for some US allies who went unnamed, saying they often treat the United States worse than its enemies.

Mr Trump's Phoenix rally was the first of three in as many days that are part of a West Coast campaigning and fundraising swing that started Tuesday evening and ends Friday afternoon with a political rally in Las Vegas.

He also will headline a campaign rally Thursday evening in Colorado Springs, Colorado.

The West Coast swing's rallies are part of a broader Trump-Pence campaign strategy of dropping the president into states a the day before or a few days ahead of 2020 primaries.

One goal is to disrupt the Democratic race by encouraging his supporters, in states where they can vote in the opposition party's primary of the GOP one that he will easily win, to cross over. Another is classic Trump: He wants to amass as many of his own primary votes as possible, even though he lacks a serious Republican challenger.

Donald Trump arrives at a Keep America Great rally in Phoenix, Arizona (AFP via Getty Images)

The president stops short of encouraging this behavior, but often mentions it on stage -- and drops in a line about his preferred Democratic nominee being Vermont Senator Bernie Sanders, a self-described "democratic-socialist."

Mr Trump was asked by a reporter as he departed Washington on Tuesday about his strategy for being in Nevada and nearby states ahead of Democrats' crucial Nevada caucuses, which will see voters pick sides on Saturday.

"Well, I'll be making a speech in Nevada, and that will be probably the day before, I guess," he said. "That seems to be pretty effective. We got more votes than any incumbent president in history, in Iowa and in New Hampshire, as you saw."

"And, in that case, I went just before, the day before, and I went the day before, in both cases, Iowa and New Hampshire," he said matter-of-factly. "So it seems to be effective."

The president announced during that impromptu gaggle on the tarmac at Joint Base Andrews in Maryland that he also will hold a rally in South Carolina before that state's Feb. 29 primary.

"I'll be going to South Carolina – they're (campaign staff) working that out now – probably the day before," he said. "But, you know, look, we have a big voice and we might as well use it."

Mr Sanders leads former Vice President Joe Biden by 24 per centage points in Nevada, with Mr Biden leading him by just over 3 per centage points in South Carolina, according to an average of polls tabulated by RealClearPolitics. Mr Sanders has taken a 10-point lead in national polls, with Mr Biden running second, according to RealClear.