After a tumultuous stretch of gaffes and falling poll numbers for Donald Trump, top GOP campaign and party officials insisted Sunday that their presidential nominee is getting back on track and will catch up with Democrat Hillary Clinton by around Labor Day.

Clinton campaign officials dismissed the idea of a changed Trump as nonsense.

"Donald Trump has been disciplined and mature. And I think he's going to get this thing back on track," said Reince Priebus, the Republican National Committee chairman.

Polls now mostly show Trump lagging Clinton by 5 percentage points or more nationally, but Priebus predicted they will tighten up and Trump will be "ahead as we move through September."

Trump's new campaign manager, Kellyanne Conway, echoed Priebus' optimism, contending that the candidate just had the best week of his campaign, "mostly because he's able to be himself, the authentic Donald Trump" and "the pivot that he's made is on substance."

Conway, who supported Trump rival Ted Cruz during the primaries, was named to her post this past week in a shake-up in which the campaign chairman, Paul Manafort, resigned and conservative media firebrand Stephen Bannon, who led Breitbart News, took over as campaign chief executive.

A new style was immediately evident as Trump, in a first, offered regrets for any remarks that had caused offense, stuck with his teleprompter at a series of events, and paid a visit to flood-ravaged Louisiana, where he briefly helped unload a truck of supplies.

That type of one-on-one interaction with voters is a staple of most political campaigning, yet something Trump had mostly avoided in favor of large rallies.

Trump also announced his first ad buys of the campaign - more evidence of an acceptance of the traditional campaign elements most experts believe he will need in order to have a shot at winning.

He made a direct appeal to African-American voters, who strongly support Clinton, and insisted he wants the GOP to become their political home as it was in the era of Abraham Lincoln.

Trump also met on Aug 20 with Hispanic supporters, representatives of a community that has been wary of the billionaire businessman's proposals to build a giant wall on the US-Mexico border.