As the caucuses in Iowa kick off later tonight, presidential candidates are doing almost everything just to get that final approval from the Iowans before they cast their initial votes as to who will be the next US President, Fox News Latino reports.

The publication revealed that Republican candidates Ted Cruz and Marco Rubio even fuelled a new feud against each other just before the primaries, with Cruz attacking Rubio and Rubio backfiring. According to the news agency, the Texan senator, Cruz, has slammed his opponent, the Florida senator, Rubio, in an ad.

According to the news outlet, Cruz launched an all-out attack against Rubio right after speaking against Donald Trump for missing a previous presidential debate. The ad reads: "Tax hikes. Amnesty. The Republican Obama," as quoted by the publication.

However, Rubio, who's not always dragged along political feuds as frequently as Trump, has also slammed Cruz. "The desperation kicks in," Rubio said of Cruz as quoted by the news agency. He added, "From my experience, when people start attacking you it's because you're doing something right."

Indeed Rubio was thinking of his most recent action towards the Iowans to be the right thing to do just before the caucuses. Time reports that Rubio's campaign distributed its own version of Cruz's mailer. The mailer was said to be designed for voters in Iowa to be encouraged or even pressured to vote later tonight.

The mailer included the voters' voting history and the phrase "Improve your score by caucusing on Monday, February 1st," according to the publication. Meanwhile, Cruz's mailer was controversial, as it reportedly accused voters to have violations in their years of voting, the news agency reports.

However, Cruz was quick to defend it, saying, "I will apologize to nobody for using every tool we can to encourage Iowans to come out and vote," he said as quoted by the news outlet.

Furthermore, the Associated Press reports that Monday night's caucuses are highly anticipated despite the weather, which has the forecast of an initial snowfall that may or may not prevent Iowans to vote.

And as the voting begins in a few hours, Rubio, who is currently behind Cruz in polls, has announced during a campaign at Northern Iowa University that voters must think hard as to who they will vote, as it will be the future of America.

"Policy differences are not enormous," he said of the GOP candidates, adding, "who gives us the best chance" in a general election, as quoted by the publication. "This election has to be about the future," he added.