(CNN) The week that gave Joe Biden a sorely needed political comeback also dealt Donald Trump some of the greatest challenges of his presidency.

As Biden's fledgling campaign roared back to life with a stronger than anticipated win in South Carolina and wave of Democratic endorsements, Trump was being tested on a level he hasn't before: facing a crisis that wasn't of his own making.

For the last several months, Trump and his aides have centered his reelection pitch to voters around a thriving economy . The novel coronavirus outbreak has sparked a public health quandary and threatened to upend that message, all while the candidate who will be Trump's chief rival for the presidency comes into clearer view.

Amid unanswered questions about how damaging the coronavirus outbreak will ultimately be, the events of the week have potentially set the stage for a general election showdown between Trump and Biden, who used his cable news victory lap after his big win in South Carolina to criticize the Trump administration for being slow to distribute test kits for the coronavirus nationwide.

Coronavirus response

When it comes to coronavirus, Trump has often seemed on a different page from health officials in his own government. He has been repeatedly corrected by top health officials on the speed of developing a vaccine, including during a meeting Monday and later after a visit to the National Institutes of Health.

Vice President Mike Pence, flanked by scientists and public health experts rather than political spinners, is frequently briefing lawmakers and the press, meeting with stakeholders and experts, and even privately admitting early missteps. Without proof, Trump blamed former President Barack Obama's administration for slowing down diagnostic testing and dismissed death rate assessments from the World Health Organization based on his own "hunch."

Confusion over the virus has created an unpredictable stock market, with two of the best days in the Dow's history and one of its worst-ever point losses both this week.

But the Trump campaign maintains that the President's pitch to voters is still on solid ground.

"The fundamentals of the American economy are so strong -- exceedingly strong," Trump campaign communications director Tim Murtaugh told CNN, citing market rebounds this week. Amid questions of how the outbreak could impact campaigning, Murtaugh insisted the President's signature "Keep America Great" rallies will not be canceled.

Murtaugh also suggested there is a value to voters in keeping a high-profile surrogate like Pence focused more on the administration's response than campaigning. Pence, who traveled to Minnesota and Washington state with task force members on Thursday, postponed a political event scheduled in Wisconsin and sent the second lady to an event in Minnesota in his stead.

"Americans want to see their elected leaders doing their jobs," Murtaugh said.

Biden's ascendance

Biden's climb back to the top of the Democratic field alongside Vermont Sen. Bernie Sanders could also force a shift in strategy for the Trump campaign, which has cast the 2020 election as a choice between a roaring economy and socialism, though Trump's aides have argued they can still make that argument if Biden is the nominee.

Biden "is not a moderate candidate," Trump's communications director told CNN, citing his positions on gun control, healthcare and the Green New Deal.

"We truly view it as a heads we win, tails they lose situation," Murtaugh said of the consolidated Democratic field. "The President is itching for an opponent. We just want to know who it's going to be."

Privately officials have remained most concerned about a Trump-Biden matchup. Those fears dwindled some as Biden's campaign seemed to recede, but they have returned since his comeback last Saturday. The campaign has continued internal polls to give them an idea of how the President would perform against Biden in states they view as crucial to victory in November like Michigan, Pennsylvania and Wisconsin.

Officials believe Biden may get a boost in these states once the Democratic Party has coalesced around a candidate.

While there hasn't been much public polling released since Biden's Super Tuesday victories , there are some indications that Biden would present Trump with a stronger reelection challenge than Sanders.

A Quinnipiac poll of registered voters in swing states conducted last month shows Biden with slightly larger margins against Trump than Sanders in Pennsylvania and Michigan. Trump edges Sanders and Biden in head-to-head matchups in Wisconsin 50 to 43% and 49 to 42%, respectively.

There are questions as to what kind of a candidate Biden could be in a general election in light of his performance at the beginning of the Democratic primary season.

"He could be very formidable. He could also be a disaster," a GOP strategist said, questioning Biden's long record as a Washington insider.

When it comes to attacking potential rivals, the campaign is still taking cues from the candidate.

"Ultimately we follow the President's lead," Murtaugh said. "He is the communications director and the campaign manager and all of those things rolled in. We'll follow what the President does."

As Biden surges, Senate Republicans are also sharpening their investigations involving Hunter Biden's work at a Ukrainian energy company. While Republicans publicly insist their efforts have nothing to do with Biden's campaign, they are using their powers in the Senate to look into a host of matters that they believe could shine negative light on the former vice president -- and help Trump as the race heads into a crucial period.

Trump and his allies have repeatedly made unfounded and false claims to allege that the Bidens acted corruptly in Ukraine.

"That will be a major issue in the campaign," Trump said during an interview on Fox News this week regarding Burisma. "I will bring it up all the time, because I don't see any way out."

Sen. Ron Johnson, a Wisconsin Republican, is leading the charge for an investigation into Hunter Biden's work at the Ukrainian energy company.

The investigation has the support of Senate Majority Leader Mitch McConnell, who told Fox News Biden's work is "worth taking a look at."

The Bloomberg factor

Former New York City Mayor Michael Bloomberg dropped out of the race after a poor showing on Super Tuesday, but he could still remain a threat to the President his wealth of ads have irked. Bloomberg endorsed Biden shortly after bowing out of the race — which could be a significant boon to Biden, a candidate who has struggled with field organization and could eventually be the nominee for a party that has failed to keep up with the Trump campaign's data juggernaut.

Bloomberg's campaign has more than 2,400 staff in 43 states and territories and, now, those staffers will focus their efforts and millions of dollars on making Biden the Democratic nominee and eventual president. Bloomberg's campaign says it will try to leverage his ground and data operations to help Biden through an existing super PAC.

There are practically no limits on what Bloomberg and his super PAC can do to aid Biden, whether that's running pro-Biden ads or overseeing a field operation to assist the former vice president. The only restriction, experts say: Bloomberg and his aides cannot coordinate their spending decisions with Biden's campaign.

"As long as Team Bloomberg doesn't talk to Team Biden about what it's doing -- how it's spending Bloomberg's fortune to support Biden -- it's not subject to any limits at all," said Paul Ryan, a veteran campaign-finance lawyer who is now vice president for policy and litigation at Common Cause.

A Bloomberg apparatus aimed at turning out low-propensity voters, the GOP strategist said, "will be huge."

"All these states -- Michigan was decided by 10,000 votes, and if they're able to organize in Detroit and some of these communities and get people to vote or go vote early, that could make a huge difference."

The campaign downplayed the impact Bloomberg could have.

"A super PAC does not have the same impact as direct spending by a candidate. President Trump is going to have every single resource he needs for his reelection. This campaign is not going to be about who has more resources. We will have every penny we need and then some," Murtaugh said, adding that the election will be "about the President's record" and the economy, "versus an extreme left opponent."