In a tweet featuring a video compilation of clips from Romney's 2012 election night defeat, Trump noted that Romney could “maybe” have beaten former President Obama in the 2012 presidential run had he spent as much energy fighting Obama as he does Trump.
Romney lost the 2016 election by more than 100 electoral votes while losing the popular vote to the incumbent Obama by about 4 percentage points.
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The tweet came after the former Massachusetts governor said he was "sickened" by the conduct of Trump and others mentioned in Mueller's report, which was released publicly with some redactions a day earlier.
"I am sickened at the extent and pervasiveness of dishonesty and misdirection by individuals in the highest office of the land, including the President," Romney said in a statement posted to Twitter.