Campaigning at a high school in Pittsburgh, Clinton slammed Toomey for supporting Trump, arguing that he is putting party in front of country in a political calculation that shows he won't stand with Pennsylvania voters over his party's nominee. The comment is the clearest statement yet that Clinton will look to help Senate Democrats in the final two weeks of the campaign.
"He still refuses to stand up to Donald Trump. Now you know, a lot of Republicans have. They have had the grit and the guts to stand up and say he does not represent me," Clinton said. "But Pat Toomey heard Donald attack a grieving gold star family who lost their son in Iraq. He heard Donald call Mexican immigrants rapists. He heard him say terrible things about women, he heard him spread the lie that our first black president wasn't really born in America. Now how much more does Pat Toomey need to hear?"
Clinton added, "If he doesn't have the courage to stand up to Donald Trump after all of this, then can you be sure that he will stand up for you when it counts?"
Polling shows Toomey is in a tight race with Katie McGinty, the Democratic Senate candidate in Pennsylvania and environmental activist.
Clinton called McGinty "exactly that kind of partner we need in the Senate, but more importantly, she is exactly that kind of senator that Pittsburgh and western Pennsylvania needs."
Trump's campaign has sputtered since a 2005 video showed the businessman talking casually about actions that amount to sexual assault. A series of women have come forward and accused Trump of making unwanted sexual advances and his poll numbers, particularly in key battleground states, have suffered.
Because of this, Democrats are hopeful that they will be able to turn Trump's struggles into losses for Republicans in tight Senate races, like Toomey's.
Clinton's comments come days after her top dollar super PAC, Priorities USA, announced that they would begin airing ads against Republican Sen. Kelly Ayotte in New Hampshire and Toomey in Pennsylvania.
Ted Kwong, Toomey's communications director, responded to Clinton's comments by arguing they prove "Katie McGinty will be a rubber stamp for everything Hillary Clinton wants to do in Washington."
"Pat Toomey has been, and will continue to be be, an independent leader in the Senate on issues ranging from gun safety to ending Wall Street bailouts," Kwong added.
Introducing his running mate, Kaine reminded the crowd of the historic nature of the election, speaking about the possibility of Clinton becoming the first female president more so than usual.
Kaine talked about watching his wife Anne, mother Kathy, and daughter Annella on stage during the Democratic National Convention, and what that meant to both him and the women in his family to see a female presidential nominee.
He noted the "strong women" staff, volunteers and donors that have stood with him throughout his career.
When Clinton asked him to be her running mate, he said, "I was honored to have the chance to play the role for her that so many strong women have played for me."
"Just think about this: Hillary's mom was born before women had the right to vote. And Hillary's daughter, Chelsea, will now get to vote for her mom to be president. Now is the claim of generational progress that this country holds for all of us when we do our best work," the Virginia senator said.
"In just 17 short days, we can forever -- and I mean forever -- change the way little girls and little boys look at their future in this country, because if you can be president of the United States, you can do anything," Kaine added.