Republican nomiee Donald Trump criticised US President Barack Obama for spending a week campaigning for his Democrat rival Hillary Clinton rather than focusing on his work.The New York magnate on Thursday said Obama "does nothing but campaign" and described him as "a campaigner in chief", Efe news reported.The billionaire candidate also said the current administration is "incompetent" and called the US president "stupid".Obama was in North Carolina this Wednesday and is scheduled to return on Friday to give two separate rallies for Clinton in Fayetteville and Charlotte.These stops are part of the president's agenda this week which also included rallies in Ohio on Monday and Florida on Tuesday and Thursday to help Clinton win the election now that the polling gap has been narrowed.Until a few days ago, Clinton held a narrow but steady lead of about three percentage points in North Carolina, but the RealClearPolitics website, which makes a daily average of all polls published in the country, now reports a "tie" of 46.4 per cent between the two candidates.With 15 electoral votes, North Carolina is seen as one of the key battleground states on the night of November 8 together with Florida and Ohio, with 29 and 18 votes respectively.