Donald Trump's campaign ad spending suggests he may well be a Democratic sleeper agent

Donald Trump reached a new low yesterday by calling on the US to close its borders to all Muslims until "we can can figure out what is going on."

His comments have been met with disbelief from some quarters: many can't believe that in 2015, it's possible for someone who wants to be the leader of the free world to keep muttering things in public that even Jeb Bush says are "unhinged".

The Donald was forced to deny very early on in his campaign that he isn't in fact a Democrat sleeper agent whose mission is to discredit the Republican party after he said Mexican immigrants were rapists and drug dealers.

Now it has come to light that Trump's campaign has only spent $217k (£145k) so far in total on a series of radio ads, and nothing on television, and continues to trounce Jeb Bush in almost all state and national polls, despite the fact the former Florida governor's super PAC (private fundraising team) has dropped $28.9m on advertising - $15.5m of that on TV ads.

Campaigners supporting Marco Rubio have spent nearly $7m, according to data collated by NBC News.

That means Trump has spent less than one per cent than the littler Bush - and as the polling averages show in this graph from The Washington Post, the money is having precisely zero effect on how the candidates poll.

By way of contrast: Hillary Clinton's campaign has spent more than $6.5m on early ads, and an additional $200k has been spent by her super PAC.

Some have said that Trump's unwillingness to spend is an indicator that he's not actually serious about becoming president.

We can only hope.

More: Here's what Donald Trump said about Muslims only two months ago

More: Donald Trump has been forced to deny he is a Democratic sleeper agent