Iowa Caucuses 2016: 5 Things to Watch for in the GOP Battle

The Iowa caucuses are exactly one week away, marking the first electoral test for the three Democrats and dozen Republican candidates vying to become their party's nominees.

The top Democratic contenders -- Hillary Clinton and Bernie Sanders -- have been busy laying out their strategies to win the nominating contest. On the Republican side, for some candidates, it's do-or-die. For others, slow and steady wins the race.

Here are five things to look for in the Republican race:

1. The Battle Heats Up: Cruz and Trump

It's down to the duel of the outsiders. Tea party darling Ted Cruz and real estate mogul Donald Trump have been locked in a tight race in most recent Iowa polling.

After Trump earned a major endorsement from former 2008 vice presidential nominee Sarah Palin last week and Iowa Gov. Terry Branstad dropped a bombshell, Cruz fired back with his own, boasting support from Glenn Beck and former Texas Gov. Rick Perry, who ended his own presidential bid last year.

Cruz has taken swipes at Trump for his "New York values" while Trump has continued to raise questions about whether Cruz is eligible to be President as a "natural born citizen" due to his Canadian birth.

2. The Best Shot to Trump the Donald

Trump will be trying to hang onto a slim lead in the critical state of Iowa ahead of the caucuses.

In a Fox News poll released Sunday, the political outsider leads Cruz 34-23 percent. Sen. Marco Rubio takes third place with 12 percent.

While campaigning in the Hawkeye State, Trump insists to crowds he "really wants to win Iowa," but admits, "it's possible" he loses the critical state.

But given Trump's broad lead in New Hampshire and national polling, many of his GOP contenders see locking Iowa as the best shot to take the wind out of Trump's sails before he picks up early momentum.

3. Marco Rubio as a Dark Horse?

Rubio picked up a key endorsement from the Des Moines Register, Iowa's most influential newspaper, less than two weeks before the Iowa Caucus.

Since 1996, the candidates endorsed by the Register have gone on to become the GOP's presidential nominee.

Despite snagging the Register's endorsement, the Florida senator trails behind Texas Sen. Ted Cruz, and front-runner Donald Trump in the Hawkeye State, according to a Fox News poll released Sunday.

But whoever takes third place will try use their position to rally the establishment behind them for New Hampshire, South Carolina, and later primaries.

4. The Do-Or-Die Candidates

There's little hope for the victors of the 2008 and 2012 Iowa caucus to relive their glory days and win the Iowa caucus this year. Former Arkansas Gov Mike Huckabee and former Pennsylvania Sen. Rick Santorum are both polling in the low single digits.

This is also a critical state for former neurosurgeon Dr. Ben Carson who has lost momentum in the Iowa polls and trails behind Trump, Cruz and Rubio. Once the results are known, look for the GOP field to be whittled down from 12 candidates.

5. Forget Iowa, Focus on New Hampshire

For Chris Christie, Jeb Bush, and John Kasich, Iowa isn't the whole ballgame. Instead, they put all their eggs are in the New Hampshire basket.

While Iowa voters tends to support social conservatives, New Hampshire voters tend to focus more on economic policy. Their moment of truth will come during the New Hampshire primary on Tuesday Feb. 9, when some candidates may not get a ticket out.

ABC News' Jeff Naft contributed to this report.