Return on investments: what do the U.S. presidential candidates have to show for their time and money?

The Democratic and Republican presidential candidates have crisscrossed Iowa in their campaign buses, stopping off for town halls and meeting voters in coffee shops, book stores and restaurants.

Some candidates have spent millions of dollars on TV advertising. By the time Iowans vote on Feb. 1 in the Democratic and Republican caucuses, a staggering 60,000 TV ads will have aired during the current cycle – with nearly a third of those aids aired in the weeks leading up to the big day, according to analysis by the Des Moines Register.

These six graphs look at how those investments of time and money have translated in to popular support.

Democratic candidates

Takeaways

The Hillary Clinton campaign and Super PACs – political action committees that can raise unlimited money and spend as they see fit, so long as they do not co-ordinate with the candidate's official campaign – have spent double the amount in TV ads compared to candidate Bernie Sanders and the groups supporting him. But the outcome is more or less the same: the two candidates are running virtually neck-and-neck in Iowa.

That in itself is a big storyline in the 2016 campaign: how Mr. Sanders has narrowed the gap between himself and Ms. Clinton. Just months ago, Ms. Clinton was polling more than 20 percentage points ahead of Mr. Sanders in Iowa.

Polls in Iowa can be volatile and caucus night can throw up surprises. A week before the Democratic Iowa caucuses in 2008, Ms. Clinton was leading in the polls, according to an average of polls in Iowa by the RealClear Politics website. Instead, Ms. Clinton finished in third place on caucus night, behind John Edwards and winner Barack Obama. Iowa hobbled Ms. Clinton's presidential campaign eight years ago. This time around, the question facing the Clinton campaign is: Does caucus night propel her White House bid, or hobble it once again?

Sensing an opportunity to win Iowa, the Sanders campaign has stepped up its ad spending. According to Kantar Media's CMAG, which tracks advertising, the Sanders campaign outspent the Clinton campaign $4.7-million to $3.7-million in the first part of January.

And finally, Martin O'Malley, former Maryland governor and Baltimore mayor, gets first prize for most days spent in Iowa. That will not, however, win him the Iowa caucuses.

Republican candidates

Takeaways

The Donald Trump formula is impressive: Spend no money on TV ads in Iowa and still finish 2015 at the head of the GOP pack.

Now, let's take a look at the outcome of the Jeb Bush campaign and its Super PAC: Spend nearly $9-million (U.S.) in Iowa and finish 2015 in fifth place. That kind of spending is happening elsewhere in the country in key states where voters will be going to the polls after Iowa.

The point is also noted by groups that are closely following campaign fundraising and spending.

"We're seeing a big disconnect between advertising volumes and poll numbers on the Republican side so far this year. Bush and his super PAC have spent more than two and a half times his nearest Republican competitor, Marco Rubio, and yet he sags in the polls," said Travis Ridout, co-director of the Wesleyan Media Project, in December.

"Meanwhile Donald Trump has aired zero ads and still stands atop the field in national polling, and Ted Cruz, who has aired 34 times fewer ads than Bush, is polling first in many Iowa polls," he added.

The data compiled by the Des Moines Register does not reflect TV ad spending in January. Data for that is still coming in. Some Republican candidates lagging in the polls have stepped up their ad spending in the closing weeks, but the amounts are generally less than half a million dollars.

In the case of Senator Ted Cruz, a Super PAC supporting him is reportedly behind a multi-million dollar ad buy in January that includes TV spots in Iowa, and even Mr. Trump has jumped in to the action with January TV spending in the range of $218,000, according to data compiled by The Guardian.

Mr. Bush can feel confident that his campaign and the political action committees that are supporting him sit on a staggering sum of around $130-million, according to Centre for Responsive Politics data, and that no other GOP candidate comes close to that fundraising figure. A financial war chest like that can come in handy in a long and drawn-out contest.

But so far, the return on investments – be it hiring political staff in key states or buying TV ad time – has been poor for the Bush campaign and allies.

Senator Marco Rubio has also invested heavily in Iowa with TV ad spending. If he can finish in the top three on caucus night, that is money well spent.

Mr. Cruz may not be outspending his rivals when it comes to TV ads, but he is outpacing most of the field when it comes to days spent in Iowa. In large part, that is to do with an ambitious strategy to visit all 99 counties before caucus night. He is still going strong and could play the role of spoiler on Monday.

The other takeaway: The top three candidates when it comes to days spent in Iowa have very little support in the polls to show for it. That is one of the functions of the Iowa caucuses: It serves to winnow the field of candidates.

And Mr. Trump – well, he continues to grab headlines through provocative statements at campaign events and free cable TV network news appearances.

With a report from The Associated Press