WASHINGTON — President Obama on Monday will call for a new minimum tax rate for individuals making more than $1 million a year to ensure that they pay at least the same percentage of their earnings as middle-income taxpayers, according to administration officials. With a special joint Congressional committee starting work to reach a bipartisan budget deal by late November, the proposal adds a new and populist feature to Mr. Obama’s effort to raise the political pressure on Republicans to agree to higher revenues from the wealthy in return for Democrats’ support of future cuts from Medicare and Medicaid. Mr....