WASHINGTON — As President Trump has struggled to explain the difficulty of negotiating a trade agreement with China, he has embraced a side argument: A Democratic president would only agree to a worse deal.
But not just any Democratic president.
“China is DREAMING that Sleepy Joe Biden, or any of the others, gets elected in 2020,” Mr. Trump wrote on Twitter Sunday. “They LOVE ripping off America!”
By Monday afternoon, Mr. Biden, making his first trip to New Hampshire since entering the 2020 race, was happily returning fire, criticizing the Twitter-borne blur of threats and flattery Mr. Trump had aimed at Beijing. “He’s going about it all the wrong way, a lot of bravado, no action,” the former vice president told reporters.
It is just the sort of fight Mr. Biden has been spoiling for: a head-to-head contest with the incumbent on an issue that elevates Mr. Biden into a statesmanlike role, well above the Democratic primary fray and all the sniping candidates and liberal litmus tests therein.
For Mr. Trump’s advisers, it was one more example of the president’s inability to resist offering what amounts to an in-kind contribution to a Democrat who, according to their own polling, is positioned to soundly defeat them next year.
The president, though, has told advisers he believes he can portray Mr. Biden, a longtime Washington veteran, as representative of an ossified political class the same way he did Hillary Clinton, wounding him with enough attacks and put-downs that Mr. Biden will either stagger into the general election or collapse in the primary.
In the three weeks since Mr. Biden announced his candidacy, Mr. Trump has tried out two nicknames on him, accused his opponent and family members of corrupt dealings with Ukraine (prompting a coordinated Democratic response) and argued that he’s naïve about the threats America faces.
Early this month, as Mr. Biden began his campaign with the endorsement of the firefighters union, Mr. Trump unleashed a barrage of almost 60 tweets and retweets about his own support from rank-and-file union members, signaling his anxiety about Mr. Biden’s standing with a crucial constituency. Aides have said that Mr. Trump is keenly aware that he won in 2016 with support from union voters who did not follow their leaders in backing Hillary Clinton.
But after all that, he then likened Mr. Biden’s bid to his own 2016 campaign, in which Mr. Trump never relinquished the lead after ascending in the polls, and suggested Mr. Biden would probably be the Democratic nominee.
Mr. Trump’s attacks on Mr. Biden have defied the pleadings of his own aides, who think almost any other candidate would be easier to defeat, and left Republicans puzzled while delighting Biden supporters.
“It just shows everybody that the vice president is the candidate Trump is most concerned about,” said Representative Cedric Richmond of Louisiana, a Biden supporter, adding with evident relish: “He just can’t help himself during executive time.”
Matt Gorman, a veteran of past Republican presidential campaigns, said that Mr. Trump was simply handing Mr. Biden a gift.
“In a Democratic primary, attacks from President Trump are the best thing that can happen to you,” Mr. Gorman said. “It elevates you, gives you a huge fund-raising boost and sucks the oxygen from your competitors.”
The president’s drumbeat of attacks on Mr. Biden have also gotten the attention of congressional Republicans, who would prefer a more easily caricatured boogeyman on top of the Democratic ticket next year. “Bernie Sanders is the perfect guy for us,” said Chris LaCivita, a longtime Republican strategist. “He looks like the professor out of ‘Back to the Future’ and is a hard-core socialist.”
Mr. Trump’s offensive has also hastened calls by G.O.P. officials to bring together White House aides, Trump campaign officials and Capitol Hill Republicans in a gathering similar to one last year at Camp David, according to a senior Republican Senate official.
Yet some Democrats, having witnessed how Mr. Trump lampooned and eventually bulldozed the Republican field in 2016, are nervous that Mr. Trump has shrewdly chosen to define Mr. Biden as the front-runner early on, identifying him as the greatest threat in a general election.
Republicans at the super PAC supporting Mr. Trump have echoed this theory, telling people in recent weeks that the party must begin eroding Mr. Biden’s credibility now and portray him as the picture of a rotten status quo, according to an official at the organization.
Officials at the super PAC, America First Action, have argued that doing so would allow Mr. Trump to maintain the outsider image he cultivated during the 2016 campaign, never mind that he is an incumbent president.
But some Republicans close to Mr. Trump paint a more simplistic portrait of the president’s actions: That he has simply been consuming cable news coverage about Mr. Biden, and firing off tweets based on the coverage and polling on the Democratic race he hears about on the air. And senior Trump campaign aides have recently told other Republican officials that they would rather not face Mr. Biden in the general election, according to one party figure familiar with the conversations.
Mr. Trump’s aides are not united on the best way to undercut Mr. Biden. His initial strength in the Democratic primary has surprised them.
A recent survey of battleground states conducted for the Trump campaign by a leading Republican pollster, Tony Fabrizio, showed Mr. Biden handily beating Mr. Trump, according to three people briefed on the results. Senator Bernie Sanders did not fare as well against Mr. Trump in the poll, but also was besting Mr. Trump head-to-head in key states, these people said.
Separately, Republicans who are hoping to rescue Senator Martha McSally of Arizona, one of the party’s most imperiled incumbents, have found Mr. Biden leading Mr. Trump in that state, which no Democratic presidential candidate has carried since 1996.
Mr. Trump has been told about his campaign’s polling, although it was unclear how extensive a briefing he was given. Still, his aides and allies have urged him to stop throwing attention to Mr. Biden, arguing that it is better to have the Democrats fight it out and weaken one another over the course of their primary.
”The campaign must force Biden back into the Democratic primary,” said Stephen K. Bannon, the former White House chief strategist. “They’ve allowed him to start a general election strategy unscathed by a potential bear pit created by the populist left. Sanders and Warren are your first lines of defense — and they must be weaponized to attack, especially on China.”
Asked about the president’s focus on Mr. Biden, a Trump campaign spokesman, Tim Murtaugh, said they “view the Democrat field as one big socialist organism with more than 20 heads, Joe Biden included.” He then hammered Mr. Biden on trade agreements, manufacturing job losses and his comments on the campaign trail in Iowa playing down China’s threat to the United States.
Mr. Trump’s unrelenting attacks have only prompted the former vice president to keep baiting the president, inserting lines into his stump speech he hopes will be picked up by the news media and create a new cycle of attack-and-response.
On Monday, in New Hampshire, Mr. Biden invoked Mr. Trump’s stinging characterization of the state’s opioid difficulties.
“One of the worst statements he made when he was on the phone with the president of Mexico was to refer to New Hampshire as a quote, ‘drug-infested den,’” Mr. Biden said in Manchester.
Mr. Trump, who has called Mr. Biden “Sleepy Joe” and “SleepyCreepyJoe,” has in turn seized on one of the former vice president’s gaffes, noting that Mr. Biden referred to Prime Minister Theresa May of Britain as Margaret Thatcher. “That was a beauty,” the president told Politico last week.
On Tuesday, at a taxpayer-funded and ostensibly policy-focused energy forum in Louisiana, the president asked “What the hell happened to Biden?” and compared him unfavorably to Mr. Sanders.
“Bernie’s crazy, but he’s got a lot more energy than Biden so you never know,” Mr. Trump said.
But it is not Mr. Sanders who is the focus of attention at the Republican National Committee, which is often directed to act by White House officials. The committee chairwoman, Ronna McDaniel, has used her Twitter account to target Mr. Biden multiple times, attacking him for letting “China get away with unfair trade practices” just hours before the president spoke Tuesday.
And last week, the R.N.C.’s research department blasted out an email to reporters with a mountain of opposition research headlined: “Joe Biden Has Made A Career Of Being Soft On China.”
Perhaps most striking, Mr. Trump’s personal lawyer, former Mayor Rudolph W. Giuliani of New York, even sought to travel to Ukraine to meet with the country’s president-elect and urge him to pursue an inquiry into the role of Mr. Biden’s son, Hunter, in a gas company owned by a Ukrainian oligarch.
Mr. Giuliani only backed off after Democrats cried foul. (The Democratic pushback against the aborted mission to Kiev was coordinated by a Biden adviser, Antony J. Blinken, according to a senior Democratic official.)
Mr. Trump himself was surprised by Mr. Giuliani’s proposed trip, according to Republicans briefed on his thinking, but he has hardly taken a hands-off role on Hunter Biden: The president said last week that a potential Department of Justice investigation into the matter “would be an appropriate thing” for him to discuss with Attorney General William P. Barr.