Now that the U.S. Senate has voted 69-27 to allow states to compel online retailers to collect sales tax even when they have no physical presence in a state where a shopper is located, will we see a stronger pushback? Politicos expect a tougher fight in the House of Representatives. Lobbyists including former lawmakers and governors have been hired by supporters of the bill to push it to victory and into law. President Barack Obama has already declared his support for the measure. The “Marketplace Fairness Act” has the support of some of the nation’s largest retailers—online giant Amazon.com backs it—as well as many traditional “brick-and-mortar” retailers, including the world’s largest, Walmart. Smaller brick-and-mortar retailers also support the bill, arguing it is unfair they must charge sales tax on all their sales while online and catalog retailers must charge sales tax only on sales that originate in states where they have a physical presence. That difference stems from a 1992 U...