AP

With his approval rating again climbing to post-impeachment high, Donald Trump mocked his Democratic challengers by contending his campaign's internal polling shows him winning a second term.

The president used a tweet to call his campaign's polling "REAL," contending those surveys show him "beating all of the Dem candidates".

"The Fake News Polls (here we go again, just like 2016) show losing or tied," he tweeted, referring to polls in the last presidential election cycle that up until Election Day showed Mr Trump trailing former Secretary of State Hillary Clinton, the Democratic nominee that year.

Mr Trump continued to make public predictions that he will defeat any of the remaining Democratic nominees, writing from Las Vegas on campaign tour: "Their polls will be proven corrupt on November 3rd, just like the Fake News is corrupt!"

His prediction and tweet came as an average of nearly 10 widely respected public opinion polls put him at his most popular since the House impeached him and Senate acquitted him on two charges of misconduct.

Forty-six per cent of Americans approve of the job he is doing, according to a RealClearPolitics average of nine polls. That's against 51 percent who disapprove, 7 points off the highest amount of voters who have objected to his job performance.

A Rasmussen Reports survey included gave the president his highest approval figure, 50 per cent, followed by a poll conducted by The Hill and HarrisX, 49 percent. He got the lowest marks in a Politico/Morning Consult poll, 43 per cent, followed by a NPR/PBS/Marist College poll, 44 per cent.

National polls of hypothetical one-on-one polls between Mr Trump and the top six Democratic candidates show each one defeating the incumbent in the popular vote. Several of those, however, are within most polls margins of error - and Ms Clinton maintained a sizeable lead in each survey last time only to be defeated in the Electoral College.

Mr Trump and his campaign aides have made clear they again are running a campaign focused on securing the 271 Electoral College votes needed to secure the presidency.

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The president and his team are banking that a strong economy will make him tough to beat come November. He frequently boasts about low unemployment and booming retirement accounts at official White House public events and campaign rallies, ignoring the part of the post-2008 economic recovery that began under President Barack Obama.

The president last weekend knocked Mr Obama and some of his former aides for pointing that out, setting up a major issue for the 2020 campaign.

A recent Gallup poll showed more of those surveyed, 62 per cent, gave Mr Trump credit than Mr Obama, 51 per cent.