WASHINGTON (AP) — As a presidential candidate in 2016, Donald Trump seized control of the White House race and never let go. He masterfully defined and denigrated his opponents with cutting nicknames and a say-anything debate style, and repeatedly drew his rivals into the controversies he created.

That's proven far more difficult for Trump in the 2020 race. Though he may still be the most visible and visceral force in the White House contest, he has repeatedly struggled to control the contours of the campaign against Democrat Joe Biden.

The president's attacks on Biden have been scattershot and inconsistent, frustrating some Republicans who believe he has squandered repeated opportunities to define his rival. His efforts to move past the coronavirus pandemic and onto issues he views as more favorable for his reelection prospects, including law enforcement and the economy, have failed to convince many voters that the public health crisis is any less of a concern or that his leadership during the pandemic has been effective.

Even Trump's rollout of Judge Amy Coney Barrett as his Supreme Court nominee on Saturday, a pick aimed at energizing conservative voters, was overshadowed the very next day by bombshell revelations in The New York Times about his personal finances.

Tuesday's first presidential debate between Trump and Biden offers the president one of his last opportunities to reshape the race and color voters' impressions of the former vice president. But with just five weeks until Election Day, voting already underway in some battleground states, and partisan views among many voters deeply entrenched, some Republicans say Trump may have effectively run out of time.

"Donald Trump is essentially facing three enemies in this campaign: He's facing the coronavirus, he's facing Joe Biden, and he's facing the calendar," said Neil Newhouse, a Republican pollster.

Few leaders in either party are ready to truly count Trump out, particularly given that polls broke late for him in his 2016 contest against Hillary Clinton. And in the lead-up to Tuesday night's debate, Trump has previewed a broad attack on Biden's record, his character and his mental acuity.

But his messaging has inherent inconsistencies.

Sometimes Trump paints Biden as a far-left candidate; at other times he argues that while Biden is more moderate, he would be controlled by his party's most liberal factions. Trump has aggressively argued that his 77-year-old rival has lost a step and isn't up for the job; yet in talking points Trump's campaign sent Republicans on Monday, they warned that Biden's abilities in the debate should not be underestimated.

Some of the president's supporters say they remain confident Trump has both the time and the political skill to overtake Biden in this final stretch.

"President Trump has plenty of ready-made ammunition he has been using effectively on the campaign trail," said Ed Brookover, a Republican strategist who advised Trump's 2016 campaign before being ousted during the general election. "They will resonate as people learn more about Vice President Biden."

But privately many Republicans are perplexed that Trump, who skillfully identified and preyed on his rivals' weaknesses in 2016, seems to still be grasping for the most effective ways to define Biden at this late stage of the campaign. Some warned the campaign earlier this summer that they were at risk of wasting the advantages of incumbency: the months and the money that a sitting president can typically use to test out messages against a rival ahead of the fall campaign.

Indeed, recent incumbents who won second terms effectively used the spring and summer before the election, when their eventual rivals were still finishing primary contests and just beginning to build out for a general election, to define their opponents for voters before they could do so themselves. President George W. Bush used the time to cement the impression that Democrat John Kerry was a flip-flopper. President Barack Obama launched an advertising barrage casting GOP challenger Mitt Romney as a wealthy, out-of-touch corporate raider.

"The average voter needs to hear the same message eight times to even remember it, let alone believe it, and most voters don't spend their days consuming their political news," said Ben LaBolt, a former Obama campaign and White House aide. "Trump has thrown a lot of darts at the board, but none of them have stuck."

It's not for a lack of trying on Trump's part.

On Twitter and at campaign events, the president has for months lobbed an array of attacks on Biden, targeting his lengthy career in Washington and floating unsubstantiated claims about his son Hunter's business ties to Ukraine. With time running out, some of Trump's attacks have become more spurious, including an assertion that Biden may be on drugs during the debate. There is no evidence to support Trump's claim and it appears to be an attempt to preemptively explain away a strong performance by his Democratic opponent.

So far none of the attacks have had the resonance of Trump's scathing critiques on his 2016 GOP primary rivals and, ultimately, Clinton. He hammered Clinton relentlessly as a "crooked," calculating and secretive politician — attacks that had added resonance with some voters late in the campaign after WikiLeaks revealed hacked emails detailing the inner workings of her campaign and then-FBI Director James Comey revived questions about a private email server she used as secretary of state.

"He was successful in making the race more about Hillary Clinton in 2016 than it was about himself," said Newhouse, the Republican pollster. "This year it's been a struggle to do that."

__

Editor's Note: Julie Pace has covered the White House and politics for the AP since 2007. Follow her at http://twitter.com/jpaceDC