US President Donald Trump said his voting base was "stronger than ever" as he attacked "phony polling" that showed some of his his core supporters slipping away.

In doing so Mr Trump contradicted his own Counsellor, Kellyanne Conway, a polling expert, who admitted support from "Trump voters" was "down slightly and needs to go up".

Mr Trump spent his 200th day in office at his golf course in New Jersey in what White House officials called a "working vacation".

Writing on Twitter he said: "The Trump base is far bigger and stronger than ever before despite some phony Fake News polling. Look at rallies in Pennsylvania, Iowa, Ohio and West Virginia.

"The fact is the Fake News Russian collusion story, record Stock Market, border security, military strength, jobs, Supreme Court pick, economic enthusiasm, deregulation, and so much more have driven the Trump base even closer together. Will never change!"

It followed a poll by Quinnipiac University showing his overall approval rating down to a new low of 33 per cent, from 40 per cent on June 29.