What we learned from Iowa

The races for the Republican and Democratic presidential nominations are taking shaping now that Iowans have had their say.

Hillary Clinton won the contest for the Democratic Party's presidential nomination by a razor-thin margin. The former American secretary of state and first lady beat the Vermont senator Bernie Sanders by as few as four delegates' votes - the closest result in the history of the Democratic caucus in Iowa.

Republicans in the rural midwestern state backed the ultra-conservative Ted Cruz for their party's nomination, leaving long-time frontrunner Donald Trump in second place, just ahead of Senator Marco Rubio.

In some cases, these results confirmed conventional wisdom. In others, they totally reshaped it.

Here are five things we learned after a remarkable evening in America's heartland:

1. Donald Trump isn't untouchable

For the past few months it seemed as though the New York real estate mogul had become an unrivalled political savant. Every move he made, no matter how questionable, only strengthened his standing among conservative voters.

That bubble, however, has burst. Despite leading in the Iowa polls for the past several weeks, Mr Trump was bested by rival Ted Cruz on caucus night. In the end Mr Trump's much-heralded cadre of new voters didn't show up in the predicted numbers and Mr Cruz's formidable ground game, backed by strong evangelical support, carried the day.

This hardly means it's the end for Mr Trump. He may well hold onto his large lead in New Hampshire, a state where the conservative voters often embrace the renegade outsider, and find success in the Southern primaries that follow. The notion that the New Yorker could steamroll his way to the Republican nomination, however, has now been firmly dispelled.

2. Marco Rubio has given the establishment hope

Florida Senator Marco Rubio's speech in Iowa on Monday night sounded more like a victory celebration than the concession speech of a third-place finisher. By finishing with 23 percent of the vote, however - a hair's breadth from second-place Trump - Mr Rubio shattered pre-caucus expectations.

Now he's well positioned to gain new support in New Hampshire, as voters looking to stop outsider candidates Cruz and Trump rally to his side.

This is the kind of Iowa result that candidates like New Jersey's Chris Christie, former Florida Governor Jeb Bush and Ohio Governor John Kasich were dreading. They have placed all their hopes in New Hampshire, and now they'll have to face off against a man who has the political wind at his back.

The polls for Mr Rubio in the coming states haven't looked particularly encouraging, but that could quickly change. And even if he suffers setbacks in the Southern states that follow New Hampshire, he likely will have the resources to wage a long fight for the nomination.

3. The Democrats are in a dogfight

At this point it comes as little surprise that Vermont Senator Bernie Sanders and former Secretary of State Hillary Clinton finished in a virtual tie in Iowa - polls had been indicating such a result was likely.

Nevertheless, the outcome marks a significant achievement for Mr Sanders, who was polling in single digits in Iowa six months ago.

Mrs Clinton is simply not going to be able to deliver the knockout punch to her rival the way she once had hoped. Instead, she faces a likely defeat in New Hampshire - where the Vermonter is strong - and then a protracted fight across the country that could last at least through March.

She still has the greater financial resources and a much more developed campaign infrastructure, but she had those advantages in Iowa as well. The electorate will change, however - becoming more moderate and more ethnically diverse. There is more hospitable ground ahead for Mrs Clinton - but a nomination victory, if it comes, will take time to realise.

4. Ted Cruz is built to last

If Mr Cruz had been defeated in Iowa it would have been a devastating blow to his campaign. He had raised expectations of a victory in the caucuses and heralded it as proof that he could build a coalition of evangelical, grass-roots Tea Party and libertarian voters.

As it turns out, that coalition exists - and it will likely re-emerge after New Hampshire, as South Carolina and other Southern states hold their primary contests.

Mr Cruz has nearly $20m in campaign cash on hand and supporting political committees with even greater resources. He's built a political machine that can operate through the entire primary calendar and, if necessary, wage a two-front battle with Mr Trump and an establishment-backed candidate like Mr Rubio.

In his victory speech on Monday night, Mr Cruz credited his grass-roots organisation - as he should - but he also gave Republicans a look at a more moderate, general-election version of himself. He'll need to convince his party that he is a candidate who can beat the Democrats in November. This was his first step toward making that pitch.

5. The field is about to thin dramatically

Democrat Martin O'Malley is gone, as is Republican Mike Huckabee and - in all likelihood, Rick Santorum.

On Monday night rumours abounded that Ben Carson was poised to exit. Although his camp quickly denied this, the retired surgeon's 9 percent performance in a state that once viewed him as a front-runner likely means the end is near.

Carly Fiorina's bid is on life support, and Rand Paul - at one point thought to be a contender for the nomination - garnered less than 5 percent, a far cry from his father's 21 percent in Iowa just four years ago.

New Hampshire will likely cull the herd even further, threatening the future of candidates like Mr Bush, Mr Christie and Mr Kasich if they can't slow Mr Rubio's momentum.

The Republican race for the nomination isn't likely to end anytime soon, but there are about to be a lot fewer candidates on the debate stage in the coming weeks.

- BBC