Hillary Clinton, the U.S. Democratic candidate for president, gave a foreign policy speech Thursday that challenged the Republican candidate, Donald Trump.

Clinton is a former U.S. Secretary of State and the leading candidate for the Democratic Party's presidential nomination. Trump, a Republican, is her likely opponent in the presidential election.

Clinton spoke during a visit to San Diego, California. She said that, if elected, her foreign policy as president would greatly differ from Trump's. Clinton said she believes in a "smart and principled" foreign policy.

She said that Trump's approach to foreign policy and other serious issues is "dangerously incoherent."

"I believe the person the Republicans have nominated for president cannot do the job," Clinton said. She said that electing Trump would be a "historic mistake" for the United States. She also called Trump "temperamentally unfit" to be commander-in-chief.

Clinton criticized Trump for his plans to build a wall to keep illegal immigrants out of the U.S., and try to make Mexico pay for it. Clinton said this would only turn Mexico into an enemy.

"We're still the last best hope for earth. We are not a country that cowers behind walls," she said.

Clinton also spoke about Trump's call to temporarily ban Muslims from entering the United States. She said the plan would be a "huge propaganda victory" for Islamic State.

Clinton said that when Trump "insults" Muslims and Mexican-Americans, he is insulting many U.S. military members from those groups.

Trump has criticized the NATO alliance as obsolete and requiring too much money from the United States. Clinton said that if NATO is weakened, the U.S. will be increasingly isolated, and countries like Russia will be "celebrating."

In his usual way, Trump reacted quickly to the speech on social media. The Republican hopeful sent out tweets live as Clinton spoke.

"Crooked Hillary no longer has credibility -- too much failure in office. People will not allow another four years of incompetence!" one tweet read.

"Bad performance by Crooked Hillary Clinton! Reading poorly from the telepromter! She doesn't even look presidential!" said another.

I'm Bryan Lynn.

Bryan Lynn reported this story for VOANews. George Grow was the editor.