Winkler is a nationally recognized expert on American constitutional law. A frequent contributor to The Huffington Post and The Daily Beast, his commentary and opinion pieces have been featured in the New York Times, the Wall Street Journal, The New Republic, the Los Angeles Times, CNN, National Public Radio, The Tavis Smiley Show, and The National Law Journal. His writing on the right to bear arms, which is notable for its middle-of-the-road position—recognizing both the individual right to possess firearms and the legitimacy of effective gun control—has been cited by the U.S. Supreme Court and numerous lower courts. His book Gunfight: The Battle over the Right to Bear Arms in America details the importance of the right to bear arms throughout American history, while also showing how that right has been balanced with laws to enhance gun safety since the founding era. Leading gun-rights advocate Dave Kopel called Gunfight "one of the few genuinely moderate books ever written on" the right to bear arms. Winkler has also written extensively on the political speech rights of corporations, work that has also been cited by the Supreme Court. He is also known for his empirical scholarship on constitutional law issues, including a much-cited quantitative study that disproved the well accepted legal maxim that strict scrutiny—a test courts apply to determine the constitutionality of burdens on fundamental rights—is "'strict' in theory, but fatal in fact." Examining 14 years of federal court decisions, Winkler found that laws survived strict scrutiny 30% of the time and that, in at least one area of law—religious freedom—constitutional law's most rigorous test resulted in the law being upheld in nearly 60% of cases. In other work, Winkler found that federalism was a hidden factor in free speech jurisprudence, with nearly 56% of federal laws burdening core speech rights upheld, compared to 23% of state laws and only 3% of local laws. Winkler also writes in the field of legal history. In addition to Gunfight, he has scholarly articles on the origins of campaign finance law, the women's suffrage movement, and the regulation of political parties. He has also written on affirmative action, the right to vote, judicial independence, and international sanctions. Along with Pulitzer Prize-winning historian Leonard Levy and UCLA School of Law professor Kenneth Karst, Winkler edited the six-volume Encyclopedia of the American Constitution.