Newly revealed text messages have shown that senior FBI officials who had been investigating Donald Trump's presidential campaign sent messages claiming that Hillary Clinton "just has to win".

The New York Times published the messages from 2016 which demonstrate that officers were concerned about the impact that a potential Trump victory could have.

The messages were primarily between counterintelligence agent Peter Strzok and senior FBI lawyer Lisa Page and have been condemned by senior Republicans as showing that an investigation into alleged links between the Trump campaign and Russia is not impartial.

The conversations looked at various aspects of the 2016 presidential race. One viewed a Trump success as "terrifying"

They also questioned the mannerisms of Trump who, after making an apparent sexual allusion while talking about the size of his hands, was described by the agents as someone who "cannot be president".

Strzok wrote he was "scared for our organisation" and called Trump a "douche".

The messages were revealed after they were turned over to Congress.

Strzok became one of the top investigators in special counsel Robert Mueller's probe into alleged collusion between Russia and Trump campaign officials.

Mueller, a former FBI director, removed Strzok from his team after finding out about the messages.

Republicans have become uneasy with Mueller's investigation in recent weeks, and some have called on Trump to remove the former FBI boss from his post over suggestions that the probe has been politically motivated.

A number of individuals from within and outside the White House have already been charged with various offences. Michael Flynn, former National Security Adviser to Trump has pleaded guilty to a charge of making false statements to the FBI.

In October, the former chairman of Trump's presidential election campaign, Paul Manafort, was placed under house arrest after being indicted as part of the investigation into Russian collusion at the polls.

Manafort and his associate Rick Gates were indicted on 12 counts of conspiracy against the United States, conspiracy to launder money, being unregistered agents of a foreign principal, false and misleading FARA (Foreign Agents registration Act) statements, false statements, and seven counts of failure to file reports of foreign bank and financial accounts.

One of Trump's former top campaign advisers, George Papadopoulos, has also pleaded guilty to lying to the FBI during the collusion investigations.