Clinton, flanked by American flags and standing beneath a portrait of George Washington, said Trump is dividing the United States and is a far cry from Lincoln, who argued against slavery in the same chamber in 1858, famously telling the assembled lawmakers that "a house divided against itself can not stand".
An NBC/Wall Street Journal/Marist poll shows Clinton ahead of Trump by nine points, 45-36, among registered voters in Pennsylvania.
Trump tweeted the results of the poll, including a picture of the poll results showing him polling ahead of Clinton by a larger margin when asked who is more effective against the ISIS terrorist group.
In Pennsylvania, Trump is now up by two points, 43 to 41 percent.
Poll director Charles Franklin said the coming weeks will reveal if the national party conventions affect either candidates' fortunes.
In June, Clinton held a lead of 42-35 over Trump among registered voters, and 46-37 among likely voters. In Ohio, the race is tied, with both candidates at 41 percent.
Hillary Clinton and Donald Trump.
All of those leads are within the margin of error: 3.1 percentage points in Florida and Pennsylvania, and 3.2 percentage points in Ohio.
No candidate has won the White House without winning at least two of these three states since 1960, according to Quinnipiac University.
Investigators decided not to recommend charging her with a crime for her use of a private email server as secretary of state, but they panned her "extremely careless" stewardship of sensitive, classified information, and they cast doubt on several explanations she's provided to explain the controversy. Bernie Sanders of Vermont, endorsed Clinton Tuesday.
But Clinton also looked inward during her remarks, telling assembled guests that political divisions have caused fear and anxiety to fester and that she realizes she "cannot stand here and claim that my words and actions haven't sometimes fueled the partisanship that often stands in the way of our progress".
"We know the battlegrounds are going to be close till the end".
The Wisconsin Senate race has mixed results compared to June, but with Democratic challenger Russ Feingold still leading incumbent Republican Ron Johnson by single digits. Self-identified Republicans are a bit more split - 78% backed Trump, while 9% supported Clinton, 4% said they liked Johnson and 3% supported someone else.
Among likely voters, it's Feingold 49 percent, Johnson 44 percent.