The former secretary of state pounced on conflicting messages from Trump and Mexican President Enrique Peña Nieto following their meeting. Trump told the press in Mexico City that while he and Peña Nieto discussed plans to build a wall along the US-Mexico border, they did not talk about Trump's pledge to make Mexico pay for it.
Peña Nieto did not refute Trump's comment during their press conference, but he tweeted hours after that he told Trump that Mexico "will not pay for the wall."
"Trump just failed his first foreign test. Diplomacy isn't as easy as it looks," Clinton tweeted, signed with an "H" to indicate she personally blessed the message.
A campaign tweet a short time later followed up: "We are not going to criminalize, profile, round up, and deport 16 million people."
John Podesta, her campaign chairman, said in a statement: "It turns out Trump didn't just choke, he got beat in the room and lied about it."
The Clinton campaign also released a web video
on Wednesday that accused Trump of lying about his trip to Mexico and sarcastically called him the "Great Negotiator."
And after Trump delivered a hardline immigration speech, the Democrat's campaign quickly condemned it.
"In his darkest speech yet, Donald Trump doubled down on his anti-immigrant rhetoric and attempted to divide communities by pitting people against each other and demonizing immigrants," said Lorella Praeli, Clinton's national Latino vote director, in a statement.
She added: "He showed us, very clearly, what's at stake in this election by painting a picture of his idea of America: one in which immigrants are not welcomed and one in which innocent families are torn apart."
The Clinton campaign's tough language about Trump came after the former secretary of state on Wednesday urged veterans at an American Legion conference to reject the mogul's view of the world, arguing he doesn't have what it takes to build and maintain alliances.
Though Clinton was more subtle in her attacks on Trump in front of the audience of veterans, she did blast the businessman-turned-politician for what she said were his insults toward the military, attacking the family of a soldier killed in action and being too cozy with Russian President Vladimir Putin.
Building alliances and trust with other nations, Clinton said, takes "more than a photo op, it takes consistency and reliability."
"You don't build a coalition by insulting our friends or acting like a loose cannon. You do it by putting in the slow, hard work of building relationships. Getting countries working together was my job every day as secretary of state," Clinton said. "It's just like building personal relationships -- people have got to know they can count on you -- that you won't say one thing one day and something totally different the next."
Clinton then added that building those relationships "certainly takes more than making up for a year of insults by dropping in on our neighbors for a few hours and flying home again."
The former secretary of state pledged on Wednesday that, as president, she would "never, ever disrespect Gold Star families who have made the ultimate sacrifice for our nation or prisoners of war who endured so much in our name."
Trump blasted the Khan family after they spoke at the Democratic National Convention this summer. Khizr Khan, a Pakistani-American lawyer and the father of the late Humayun Khan, powerfully hit Trump during his speech and Trump responded
by questioning his family's motives. Earlier in the campaign, Trump also downplayed the heroism
of Arizona Sen. John McCain, a POW, citing his capture during the Vietnam War.
"To insult them is just so wrong," Clinton said. "And it says a lot about the person doing the insulting."
Clinton continued her outreach to Republican voters as well Wednesday, pledging before a somewhat muted crowd to "be a president for Democrats, Republicans, independents, for people who vote for me, for people who don't, for all Americans."
Trump's campaign responded to the speech by saying that Clinton has proven that she is "fundamentally unequipped to further the national security interests of the United States and stand up for our veterans."
"Those who have served and wear the uniform today deserve to have a commander in chief who is looking out for them rather than donors and corrupt bureaucrats," said Matt Miller, director of Veterans for Trump. "Only Donald Trump and Mike Pence have a detailed plan to fundamentally improve both the (Department of Veterans Affairs) and the way veterans are treated in this country."