The time for a turnaround is tightening.

The problem for President Trump is not just that he's had a bumpy beginning in office – so did John Kennedy and Bill Clinton, among others. It's also that he's heading into the second half of his first year in the White House without yet applying lessons learned the hard way about imposing discipline, compartmentalizing scandal and adjusting course.

"It's a presidency under siege," Leon Panetta, a Democratic elder who helped rescue another embattled White House as chief of staff for President Clinton, said in an interview. "Unless some dramatic changes are made, I think there's a real question about whether the presidency can survive."

The first six months of Trump's presidency were brutal.

The next six months could well be worse.

As the midpoint of his crucial first year approaches Thursday, a steady stream of disclosures about contacts between Trump's team and Russians who may have involved in election meddling has transfixed Washington. When it comes to issues closer to Americans' lives back home, the president is still in search of his first major legislative victory on a core campaign promise — to replace Obamacare with a "wonderful" new health care system, say, or to cut taxes, or to launch a massive investment in infrastructure, or to build a wall across the Mexican border.

Allies, critics and historians are watching the clock. While presidents are elected to four years in office, all political time is not created equal. For his modern predecessors, the first year or so after an election is when campaign promises typically are met and signature legislation passed.

An ABC News/Washington Post poll released Sunday showed Trump's standing, which already had set record lows, deteriorating more. His 36%-58% approve-disapprove rating is down six percentage points from the 100-days mark and the lowest for any president at six months in the 70-year history of polling.

What's alarming for those who want the president to succeed is this: The political moment may never be better for Trump than it is now.

He continues to hold relatively solid support from the voters who put him in the White House, and he has the benefit of a House and Senate both under GOP control. Republicans fear and Democrats hope that won't be true after the midterm elections next year.

Even so, Trump is having the most difficult first year of any modern president, says Barbara Perry, director of presidential studies at the University of Virginia's Miller Center. "It comes from his unprecedented lack of government or military experience, and his unprecedented personality," she says.

On the theory that the first year — not the first 100 days — represent the make-or-break time, The Miller Center launched The First Year Project in October 2015 to study the challenges the new president faces in the future and the experiences of his predecessors in the past.

Perry rates two modern presidents as having "A-plus" first years: Franklin Roosevelt, who tackled the Depression by pushing his New Deal programs through Congress with dizzying speed, and George H.W. Bush, who skillfully oversaw the end of the Cold War. She gives George W. Bush an A for delivering on campaign promises of a tax bill and education reform, and for his response in the months after the 9/11 terror attacks.

But she gives Kennedy a B-minus, though with credit for applying lessons he learned during the Bay of Pigs fiasco, and Clinton a C-minus, for early chaos and controversy over appointments and priorities.

And Trump?

"Maybe in the D-plus realm," she says.