WASHINGTON — Vice President Kamala Harris is expected to announce economic policy proposals aimed at helping small businesses during a campaign speech Wednesday in New Hampshire. The Democratic presidential candidate will stump in Portsmouth for expanding the tax deduction to $50,000 on business start-up costs, up from $5,000, a campaign official said on background Tuesday. Harris will also propose a standard deduction for businesses as a way to simplify tax filing for entrepreneurs. Congress writes the nation’s tax laws, so any changes will hinge on which party wins control of the House and S…