Hillary Clinton is consolidating her support among Wall Street donors and other businesses ahead of a general-election battle with Donald Trump, winning more campaign contributions from financial-services executives in the most recent fundraising period than all other candidates combined.

The Democratic front-runner has raised $4.2 million in total from Wall Street, $344,000 of which was contributed in March alone. According to a Wall Street Journal analysis of fundraising data provided by the nonpartisan Center for Responsive...