Elizabeth Warren has gained support among Democrats as a running mate for Joe Biden. WSJ’s Gerald F. Seib explores the strengths and weaknesses she could bring as Biden’s pick for vice president. Photo: Chris Carlson/Associated Press Joe Biden says he will add details to his climate plan and is likely to propose new investments, an olive branch to Bernie Sanders and his liberal allies. But in battleground states such as Pennsylvania, Republicans are already portraying Mr. Biden as a threat to the oil and gas industry. Mr. Biden has indicated he is willing to do more to address climate change, saying last month that possible areas to build on include investing in clean energy technologies and environmental justice, or policies that prevent minority communities…