Republican presidential candidate Donald Trump speaks during a campaign stop at the Allen County War Memorial Coliseum, Sunday, May 1, 2016.
Republican presidential candidate Donald Trump speaks during a campaign stop at the Allen County War Memorial Coliseum, Sunday, May 1, 2016.

U.S. Republican presidential candidate Donald Trump says the United States cannot "continue to allow China to rape our country," as he pressed his campaign pledging to reset America's relationship with the world.

Trump has repeatedly framed the trade deficit between the two countries as China taking advantage of the U.S., saying his skills as a deal-maker will erase the imbalance.

"We're going to turn it around," Trump said Sunday during a rally in the Midwestern state of Indiana. "We have a lot of power with China."

Tuesday's primary in Indiana is seen as a key contest in the race to become the Republican nominee for the November election. Multiple polls have Trump leading Texas Senator Ted Cruz, including an NBC News/Marist poll released Sunday that had Trump ahead by 15 points.

Majority of delegates

A Trump victory in Indiana would move him closer to clinching the majority 1,237 delegates he needs, while Cruz and Ohio Governor John Kasich hope they can deny him enough delegates to force an open contest at the party's convention in July.

In the Democratic race, the latest polls give former Secretary of State Hillary Clinton a small lead over Vermont Senator Bernie Sanders.

U.S. Democratic presidential candidate Hillary Cli
FILE - U.S. Democratic presidential candidate Hillary Clinton speaks at the Eagle Academy Foundation’s annual fundraising breakfast in New York City, April 29, 2016.

Clinton has a big lead in delegates that includes about 500 so-called super delegates who have pledged to support her. Sanders acknowledged Sunday that his path to the nomination is hard, but said he will work to flip those super delegates to his campaign.

Clinton said Sunday on CNN's State of the Union that she found Trump's speech on foreign policy last week "disturbing." She said the country faces "real challenges" and that turning its back on its strongest allies and touting a "secret plan" to defeat Islamic State is not a smart way to lead.

'Every move ... was wrong'

Trump defended his speech during his own interview Sunday, telling Fox News that during the past 15 years "every move we made in the Middle East was wrong."

When asked if he advocated a return to strongmen such as Iraq's Saddam Hussein, Trump said, "Isn't it too bad that we knocked them out in the first place?"

Former CIA chief and defense secretary Robert Gates told ABC News that a lot of world leaders are concerned about a potential Trump presidency.

"I think based on the speech you'd have somebody who doesn't understand the difference between a business negotiation and a negotiation with sovereign powers," Gates said. He added that he is worried Trump believes he is the "smartest man in the room" and thus does not listen to others.