Mr. Romney and his aides, meanwhile, strongly defended the so-called individual mandate, a requirement that everyone in Massachusetts have or buy heath insurance. And they privately discussed ideas that might be anathema to today’s GOP—including publicly shaming companies that didn’t provide enough health insurance to employees…

In Massachusetts, Mr. Romney didn’t include an individual mandate in his original proposal, but soon adopted the idea. The emails show his aides later came to champion it, even amid uncertainty from some Democrats. At the time, the mandate was a favored policy of the right, with the left instead pushing for government-run insurance programs.

“We must have an individual mandate for any plan to work,” Tim Murphy, Mr. Romney’s health secretary, wrote the governor and several aides on Feb. 16, 2006, in an email analyzing the latest confidential Democratic proposal, which he wrote was “unclear” about that requirement…

According to the emails, Mr. Romney personally drafted an op-ed article published in The Wall Street Journal the day before he signed the legislation. The draft, written on a Saturday, also defended the individual mandate, in different language from the final version of the piece as published.