(CNN) The most unpredictable, dumbfounding and just plain nasty presidential campaign in modern times is heading into its final full week.

Hillary Clinton, who just three days ago seemed on a glide path to a date with history, is suddenly on the defensive. The former secretary of state is again tripped up by her ill-fated decision to use a private email server during her time in office.

The FBI review of new emails from longtime Clinton aide Huma Abedin found on the computer of her estranged husband, Anthony Weiner, ensures that an issue that has dogged the Democratic nominee from the beginning of her campaign will be front-and-center through the end.

Democrats are furious at FBI Director James Comey for reviving the issue. Meanwhile, Republican nominee Donald Trump is seizing on a late and surprising chance to unite a GOP splintered by his controversial candidacy.

Some surveys suggest a tightening race, though CNN's Poll of Polls has Clinton ahead by five points.

The question now is whether this hurricane of a campaign will have a final, stunning twist -- a November surprise -- before it finally blows itself out.

What Clinton must do

Clinton thought she was in the clear when FBI Director James Comey stood before the cameras in July to announce he wasn't recommending criminal charges stemming from her use of a private email server during her tenure as secretary of state.

But now the emails are back, letting Trump gin up crowds already screaming "lock her up" with a fresh spin on long ingrained perceptions that she is dishonest, secretive and steeped in scandal.

So Clinton's campaign is aiming to turn the spotlight back on Trump, in line with her campaign-long effort to brand him as morally and intellectually unfit for the presidency.

"They're going to have to get tougher on Trump in the final week than they planned to do," CNN political analyst David Axelrod said on "State of the Union" Sunday. "They were coming in for a gentle landing and now I think you're going to see them challenging Trump both in their media and in her comments from now until the end."

On Sunday, Clinton lambasted her rival over claims he's a phony philanthropist as a preview of new character attacks to come.

Clinton will also rely on her superior ground game and polling that suggests she still has several routes to surpass the 270 electoral votes she needs.

She'll travel in the coming days to Florida and Ohio, where she's in a tight race with Trump, and North Carolina where she is leading. By winning any one of that trio, Clinton can block Trump's path to the presidency.

She'll also make a raid into Arizona, a traditionally red state that appears competitive a week out.

Clinton will dispatch former President Bill Clinton, President Barack Obama and First Lady Michelle Obama to battleground states -- leveraging her advantage over Trump, who lacks such high profile surrogates.

But there are nervous days ahead. She will now live in fear of another damaging twist to the email saga, more campaign inside gossip from the WikiLeaks hack of John Podesta's email accoun t. There's also a release of more Clinton emails from the State Department scheduled for Friday.

Coping with the Comey letter

Many Democrats believe the character issue is already baked into polls that show she is the favorite to win the election. But her plans for a smooth run in to Election Day are in tatters and her campaign has been forced into a tactical shift, unleashing its full fury on the FBI chief.

"This is something that has been tossed into the middle of the campaign. We would have preferred that that not happen, but now that it has happened," Clinton's campaign chairman John Podesta said on "State of the Union." "Mr. Comey really needs to come forward and explain why he took this unprecedented step."

But spending time attacking the FBI director is time that could be used making a closing argument for Clinton -- or attacking Trump.

For the moment, she is using a move many supporters see as yet another unfair assault on her character as a rallying cry to drive up Democratic turnout.

"There have been ups and downs in all that we have gone through over the years and even in this campaign, but I want you to know I am focused on one thing: you," Clinton told supporters in Florida on Sunday. "There's a lot of noise and distraction but really comes down to what kind of future we want."

What Trump must do to come back

In the hours after Comey's Friday bombshell, Trump and top aides could barely contain their glee. A campaign that had seemed headed for certain defeat grabbed gratefully onto the late October gift, immediately using the revelations to bolster the Republican nominee's theme that Clinton is a crook, broke the law with her email server and is symptomatic of a corrupt political status quo.

He was still laying it on thick by Sunday, reveling in the new energy the late twist lent his campaign amid signs GOP voters are uniting.

"Her criminal action was willful, deliberate, intentional and purposeful. Hillary set up an illegal server for the obvious purpose of shielding her criminal conduct from public disclosure and exposure," Trump said in Las Vegas.

But it is one thing for Trump to welcome a political gift. It's another thing for him to use it effectively. His presidential bid has been plagued by his failure to turn a trove of material detrimental to Clinton into sustained attacks.

He's been repeatedly undermined by his own indiscipline and tendency to detonate controversies that harm him more than his opponent.

"The problem with the Trump campaign all along is that they've had lots of potential material, a lot of grist for the mill that he has failed to prosecute," said Mark McKinnon, former strategist for President George W. Bush and Sen. John McCain on "State of the Union."

"Trump needs to just for once maintain a clear and constant focus for the next 10 days on the issues that can move the dial."

To mount a stunning comeback on November 8, Trump must also improve his position on the political map.

He must forge ahead in Florida and Ohio, cut his deficit to Clinton in North Carolina, capitalize on an advantage in Iowa, then find a way to put states like New Hampshire and Nevada, that went for Obama, in play. He could carve out a decisive edge by making a big blue state like Pennsylvania or Michigan competitive — though polls suggest that is a long shot.

But Trump's team must also be wondering, even as they salivate over Clinton's woes, if there is one last big shock awaiting Trump, following October Surprise controversies over claims he sexually assaulted women and an "Access Hollywood" tape exposing his lewd language that left him so far behind his rival that he starts the campaign's last week possibly too far behind to catch up.