(BBC) Virginia Senator Tim Kaine – Democrat Hillary Clinton’s newly announced presidential running mate – has made his national debut, saying “We are all Americans”.
Mr Kaine’s upbeat remarks contrasted with Republican Donald Trump’s pessimistic convention speech.
The 58-year-old moderate Democrat could appeal to Republicans who have been unsettled by Mr Trump’s candidacy.
However, the pick is seen as a blow to more left-leaning Democrats.
Mrs Clinton’s one-time rival, Senator Bernie Sanders, waged a strong campaign, championing liberal causes such as universal health care coverage.
In part, Mr Kaine’s introduction sought to assure those voters of the senator’s left-wing credentials.
“If you want to be right, be a pessimist, if you want to do right, be an optimist,” Mr Kaine said, recalling his time fighting housing discrimination as a young lawyer. “I like to do right,”
Mrs Clinton said Mr Kaine was “everything Donald Trump is not”.
“He is a progressive who likes to get things done. That’s just my kind of guy,” Mrs Clinton said of Mr Kaine.
The Trump campaign attacked the choice, dubbing the senator “Corrupt Kaine”.
As governor of Virginia, Mr Kaine accepted about $160,000 worth of gifts from political supporters, which was legal under the state’s lax gift laws.
“If you think Crooked Hillary and Corrupt Kaine are going to change anything in Washington, it’s just the opposite,” said Jason Miller, spokesman for the Trump campaign.
On Twitter, Mr Trump sought to drive a wedge between the Clinton campaign and voters who supported Mr Sanders in the Democratic primary.
Several Republicans senators praised the choice, including Arizona Senator Jeff Flake.
“Trying to count the ways I hate @timkaine. Drawing a blank. Congrats to a good man and a good friend,” he wrote.
A former mayor and governor, Mr Kaine is an experienced politician and has been thoroughly vetted. He was on the short list to be Barack Obama’s running mate in 2008.
His home state of Virginia is seen as a key battleground in the election. Vice-presidential candidates can typically give tickets a slight advantage in their home states.
Mr Kaine embraced the typical role of the running mate, attacking the rival nominee.
He called on Mr Trump to release his tax returns and criticised his business dealing including his Atlantic City casinos and Trump University.
“Trump leaves a trail of wrecked lives everywhere he goes,” Mr Kaine said.
Mr Kaine also speaks fluent Spanish, which could help the Clinton campaign’s outreach with Latinos – a key voting bloc.
On Saturday, Mr Kaine frequently spoke to the crowd in Miami in Spanish.
“Bienvenidos a todos en nuestro pais. Porque somos Americanos todos. [Welcome everyone to our country, because we are all Americans],” Mr Kaine said to cheers.
However, left-wing Democrats have questioned his stances on banking reform and abortion rights.
A Catholic, Mr Kaine personally opposes abortion and has favoured restrictions on late-term or “partial birth” abortions.
Also, he was recently among 70 senators who signed a letter urging the Consumer Financial Protection Bureau not to enact regulations that could harm community banks and credit unions.
The Democratic Party is already pushing back, enlisting President Obama to vouch for Mr Kaine.
“Like Hillary, Tim is an optimist. But like Hillary, he is also a progressive fighter,” Mr Obama wrote.
The Democrats’ four-day convention starts on Monday in Philadelphia with speeches by First Lady Michelle Obama and Mr Sanders.