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Hillary Clinton is returning to Iowa, a state that helped put Barack Obama in the White House but one that has also proven troublesome for the presidential contender.

Flanked by the heads of several major women's groups, on Friday Clinton will make what her campaign bills as a final pitch to women about the importance of voting.

Iowa has long been a thorn in Clinton’s side, derailing her first presidential bid in 2008 when she lost the state's critical caucus to Obama, and nearly doing so again this year when she eked out a razor-thin win against Bernie Sanders.

Now it has become the single hardest battleground state on the map for Clinton, who has visited only a tiny handful of times since the caucuses in February.

Obama won Iowa by six percentage points in 2012 and 10 in 2008, but Donald Trump leads Clinton by 4 points in the most recent Des Moines Register poll.

For Obama, it was personal.

"No matter what, you — the people of Iowa — had my back,” he said while campaigning in Council Bluffs in 2012. "You believed in me, and I believed in you."

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Related: Conflicting Polls, One Conclusion: Clinton is Ahead

Clinton, meanwhile, doesn’t need the state to secure the 270 electoral votes necessary to win the presidency. So it has fallen to bottom of her priority list, even behind states that are historically much more challenging for Democrats, like North Carolina, which is much more diverse.

The issue may have more to do Trump, however, than Clinton.

"Demographically, it’s a great fit for Trump," said Jeff Link, a top Iowa Democratic strategist. "We have very small Latino and African American populations and our voters skew older rather than younger."

Iowa has the largest percentage of white voters without college degrees of any battleground state — Trump’s prime demographic. It’s one of the few places were the Democrats’ support base still consists mainly of white blue-collar workers.

While Obama won the state in 2012 by portraying Romney as an out-of-touch plutocrat, this year’s GOP nominee has tapped into the state’s well-known populist streak with his anti-trade, anti-elitist message.

Meanwhile, Trump has been buoyed by a unified Republican establishment in his corner. Aside from a state senator from the northwest of the state, "we have no high profile Republicans rejecting Trump like in many other states," said Link.

Popular GOP Gov. Terry Branstad, who won 98 of Iowa’s 99 counties in 2014 to secure his sixth term, has been a vocal defender of Trump. The governor’s son, Eric Branstad, is running Trump’s campaign in Iowa.

"Thanks to the united effort here in Iowa, we will have the resources necessary to continue this program and get Republicans to the polls on and before Election Day," said Iowa GOP Chair Jeff Kaufmann in a statement.

Related: Trump's Battleground Map Makes Rosy Assessments of Toss-Up States

Working in Clinton’s favor, however, is what Democrats call a superior get-out-the-vote operation, run by veterans of Obama’s campaigns.

"If Hillary Clinton wins the state of Iowa, it’s going to be because of her ground game," said Norm Sterzenbach, the former executive director of the Iowa Democratic Party.

Clinton has kept staff on the ground since the caucus in February, and they’ve spent the past 10 months preparing for Nov. 8.

It showed in a new Quinnipiac poll, which found Clinton leading by a 34 point margin among early voters — a wider lead than Obama’s among early voters in 2012, according to Democrats.

The poll, the most recent of the state, also showed Clinton closing the gap with Trump to a tie.

Quinnipiac Assistant Polling Director Peter Brown characterized the race as a "dead heat."