JUDY WOODRUFF: With their national conventions in the rear-view mirror, the presidential candidates head out on the road to target states that could go either way, and help determine the election outcome.

Correspondent Lisa Desjardins begins our coverage.

LISA DESJARDINS: The newly minted Democratic ticket made its first post-convention campaign stop at Temple University, just minutes from last night's political party.

HILLARY RODHAM CLINTON (D), Presidential Nominee: What better place to kick off this campaign than right here in Philadelphia?

LISA DESJARDINS: For three days, the maiden bus tour will wind through the Rust Belt battlegrounds of Pennsylvania and Ohio. Clinton will be joined by her husband, Bill, as well as running mate, Tim Kaine, and his wife, Anne.

HILLARY RODHAM CLINTON: I can't think of an election that is more important certainly in my lifetime, and it's not so much that I'm on the ticket. It is because of the stark choice that is posed to America in this election.

LISA DESJARDINS: Today was about November. Last night was about history, as Clinton became the first woman to accept a major party's presidential nomination. For many of her supporters, it was an emotional night.

WOMAN: It's a trailblazer moment for me. It kind of tells me that I can be anything that I want to be when I grow up, with some hard work and dedication.

LISA DESJARDINS: Countering that narrative was Republican Donald Trump, who launched a barrage of tweets this morning, including: "Crooked Hillary Clinton mentioned me 22 times in her very long and very boring speech. Many of her statements were lies and fabrications."

Later this afternoon, Trump spoke at a campaign rally in Colorado springs.

DONALD TRUMP (R), Presidential Nominee: I watched last night. I watched Hillary Clinton.

DONALD TRUMP: What a sad, what a sad situation. And I watched her last night giving a speech that was so average.

LISA DESJARDINS: On this first official day of the general election fight, there are new concerns today over political cyber-security. Reuters reported today that the computer network used by the Clinton campaign was hacked. Also today, the Democratic Congressional Campaign Committee, a group focused on the House of Representatives, said its computers have been hacked.

The FBI is investigating and said the breaches resemble an earlier cyber-attack on the Democratic National Committee. That intrusion revealed e-mails in which party officials privately berated Clinton's primary opponent, Bernie Sanders. Clinton's team has said the hack reveals a problem with Trump and his relationship with Russia, who intelligence experts suspect of being responsible.

Trump himself denies involvement. He did publicly ask Russia to find e-mails missing from Clinton's private e-mail server, but he insists those remarks were sarcastic.

In an interview on CNN this morning, Clinton's running mate called the remarks ignorant.

SEN. TIM KAINE (D), Vice Presidential Nominee: And when Donald Trump is basically trying to encourage them to do it with respect to the U.S. election, I think an awful lot of people will see that and say that that is temperamentally disqualification for the office.

LISA DESJARDINS: It is a first volley in a campaign where national security promises to loom large.

For the "PBS NewsHour," I'm Lisa Desjardins.