The Democrat candidate's running mate provides the suburban American voters who will largely decide 2020’s race with an option that doesn’t threaten their way of life.

Washington | Four years ago when Hillary Clinton chose an obscure senator, Tim Kaine, as her running mate you could hear the crickets.

Joe Biden and Kamala Harris in an image tweeted by the Biden campaign. Supplied.

Kamala Harris, by contrast, will almost certainly energise the Democratic base and deliver a badly-needed shot of energy that will help counter Donald Trump’s attacks on "sleepy" and faltering Joe Biden.

While Harris still provides several fronts for Republicans to attack - including her strong advocacy of green energy and opposition to fracking - their early efforts in the hours after Biden revealed his pick has them struggling to find their line and length.

The incident gave Harris a brief lift in the polls and was cited as a likely barrier to Biden picking her as his running mate.

“What a contrast the Harris pick shows between Biden and Trump.".

At first blush it looks like Biden has done what he needed to do - unify the Democratic Party for the battle ahead.

A rising star, Kamala Harris is establishment-friendly, and like Joe Biden, shows cautious political instincts, even as activist energy runs through the party