During the week of July 4, as we celebrated our country's independence from the rule of kings and renewed our commitment to the rule of law, President Barack Obama explained his own unique conception of the separation of powers: If Congress wants to prevent unlawful administrative action, it should either pass a bill he likes ... or, "sue me."

Well, I tried to sue him and discovered why the president was confident he could offer such an arrogant challenge to a supposedly co-equal branch of government.

My lawsuit challenges a rule by the president's Office of Personnel Management that pretends the federal government is a small employer and allows members of Congress and their staffs to continue receiving tax-free employer contributions toward their health care. Congress specifically voted that such contributions would be unavailable so that members and staff would be in the same boat as their constituents when it came to Obamacare.

On July 14, the U.S. District Court for the Eastern District of Wisconsin dismissed my case on the legal technicality of "standing." As a result, the president has not had to defend his actions, at least not yet.

You would have thought this litigation would be unnecessary. When Congress passed Obamacare, the president got the law he wanted. According to his recent statement, there should have been no need for unilateral executive actions regarding health care.

Yet, to date, the president has made more than 20 unilateral changes to Obamacare to fix his unworkable law. The law says that the employer mandate shall apply Jan. 1, 2014; the president says 2015. The law says 50 employees; the president says 100. The law provides subsidies for an "exchange established by the state"; the president says established by the federal government, too. And on it goes.

The courts finally have considered the merits of that last unilateral change, and the president has not fared well. On July 15, in Halbig vs. Burwell, the U.S. District Court of Appeals in Washington, D.C., struck down this interpretation, and while the Fourth Circuit Appeals Court in Richmond, Va., went the other way, even its ruling admitted the administration was on shaky legal footing.

The president's overreach is not confined to Obamacare. George Washington Law School professor Jonathan Turley has testified that "President Barack Obama has crossed the constitutional line between discretionary enforcement and defiance of federal law."

The president's administrative agencies have targeted ordinary Americans through Internal Revenue Service reviews of conservative groups, enacted the president's cap-and-trade policies through Environmental Protection Agency regulations and instituted ambush election rules for unionization through the National Labor Relations Board.

Earlier this summer, the Supreme Court unanimously struck down the president's unlawful recess appointments, marking the 13th time this administration's policies have been unanimously rejected by the court. And we are just beginning to see how the president's June 2012 memorandum on "Deferred Action for Childhood Arrivals" has given unaccompanied children from Central America an incentive to embark on horrific journeys to the United States, believing that once they get here they will be permitted to stay.

The Office of Personnel Management rule is not the most egregious example of this administration's lawlessness, but it is one in which the president's unilateral actions were specifically directed at members of Congress, and thus it is one I believe I have standing to challenge. After all, it affected my health insurance, required me to take action to designate my staff and provided special treatment that drove a wedge between me and my constituents. It denied me — as a member of Congress and employer of staff — the legal status that Congress thought essential for each of its members and those who work for them.

If a member of Congress does not have standing in this case, who does? And if no one has standing to force the administration to faithfully execute the law, how can the rule of law be maintained?

Even in his order dismissing my lawsuit, District Court Judge William Griesbach recognized the importance of this case: "The violation alleged is not a mere technicality. It strikes at one of the most important safeguards against tyranny that the framers erected — the separation of powers. As James Madison explained ... 'The accumulation of all powers, legislative, executive, and judiciary, in the same hands ... may justly be pronounced the very definition of tyranny.'"

When I joined the Senate in January 2011, I raised my right hand, placed my left hand on the Bible and swore a solemn oath to support and defend the Constitution of the United States. Defending the constitutional domain of the branch of government in which I serve is an obligation of that oath.

If his standing analysis is reversed, Judge Griesbach recognized that my case will challenge the president's executive actions head on. It continues to be a landmark opportunity to address the "constitutional tipping point" we find ourselves in today. To honor my solemn oath of office, I feel compelled to exhaust every legal recourse. I will file my appeal on Monday.

Ron Johnson, a Republican, is Wisconsin's senior U.S. senator.