Naturally, Congress and its Members have an interest in litigating in federal court, for example, to vindicate their institutional priorities, to argue that the Executive is violating their legislative prerogatives, or to advance their legislative policy interests. Foremost among these doctrines is the requirement that a party seeking judicial relief from a federal court demonstrate "standing." To establish standing under that test, a party must show that it has a genuine stake in the relief sought because it has personally suffered (or will suffer) (1) a concrete and particularized and actual or imminent injury-in-fact (2) that is traceable to the allegedly unlawful actions of the opposing party and (3) that is redressable by a favorable judicial decision. The Supreme Court held that Senator Byrd and the other legislators lacked standing to bring their claims. However, Raines also determined that there was an exception to this general rule based on the Court's holding in Coleman v. Miller , "[t]he one case in which [the Court] upheld standing for legislators . Circuit have generally been hesitant to find concrete and particularized injury in cases involving individual legislators asserting institutional injuries, especially where the legislature as a whole possessed other potential avenues for relief through the legislative process. As explained below, at least two questions may arise when Congress (or a Member, committee, or house thereof) attempts to intervene to defend a statute's validity: (1) whether the executive branch's refusal to defend the statute renders the original parties insufficiently adverse to create a justiciable controversy; and (2) whether Congress possesses standing to intervene in the case. The Supreme Court has periodically considered how the adversity and standing doctrines apply in the congressional intervention context and has ultimately concluded that cases in which the executive branch declines to defend a federal statute and Congress steps in to defend the law may potentially be justiciable. Prior to the Supreme Court's 2013 decision in United States v. Windsor , one might plausibly read Chadha to stand for the limited proposition that Congress may intervene to defend an undefended federal law (albeit one that the Executive has continued to enforce) only when the judicial invalidation of that law would directly affect Congress's institutional powers, such as by eliminating Congress's ability to validly utilize a one-house legislative veto. To that end, lower federal courts have frequently permitted legislative actors to intervene as defendants in cases where the executive branch agreed with the plaintiff that a challenged statute was unconstitutional . Participation as Amicus Curiae

If Congress (or a unit or individual Member thereof) cannot participate as a full party to a particular lawsuit due to one or more of the constitutional, statutory, procedural, and prudential obstacles discussed above, it may still be able to participate in the case in a more limited capacity as an amicus curiae . Members, houses, and committees of Congress have successfully filed amicus briefs in a wide variety of cases. In the absence of such guidance from the judiciary, a congressional litigant's best strategy may be to attempt to satisfy as many of the considerations listed above—that is, to
attempt to obtain authorization to pursue the specific lawsuit in question from one or both houses of Congress; attempt to persuade the court that all possible legislative remedies would be futile; argue that the allegedly unlawful action has deprived Members of Congress of the efficacy of their votes; analogize to historical precedent in which courts entertained similar challenges by congressional litigants; demonstrate that no other litigant would possess standing to vindicate the congressional interest in dispute; and avoid framing the legal theory as a generalized grievance challenging the opposing party's implementation or interpretation of a federal statute.
Houses, committees, and Members of Congress periodically seek to initiate or participate in litigation to, among other purposes, advance their legislative objectives, argue that the Executive is violating their legislative prerogatives, or defend core institutional interests. However, the constitutionally based doctrine of "standing"—which requires a litigant seeking federal judicial relief to demonstrate (1) a concrete and particularized and actual or imminent injury-in-fact (2) that is traceable to the allegedly unlawful actions of the opposing party and (3) that is redressable by a favorable judicial decision—may prevent legislators from pursuing litigation in federal court. The U.S. Supreme Court and the lower federal courts have issued several important opinions analyzing whether—and under what circumstances—a legislative entity has standing to seek relief.
Although legislative standing jurisprudence defies easy characterization, it is possible to distill several principles from existing precedent. For example, whereas courts commonly allow individual legislators to assert injuries to their own personal interests, following the Supreme Court's seminal opinion in Raines v. Byrd, 521 U.S. 811 (1997), courts have generally (though not universally) been less willing to permit individual legislators to seek redress for injuries to a house of Congress as a whole, at least in the absence of explicit authorization to do so from the legislative body itself. The Supreme Court's case Coleman v. Miller, 307 U.S. 433 (1939), is generally understood as setting forth the lone exception, allowing individual legislators to sue when their vote has been "nullified" by some claimed illegal action. In addition, generally speaking, a congressional plaintiff cannot predicate a federal lawsuit solely on a complaint that the executive branch is misapplying or misinterpreting a statute, as litigants must demonstrate concrete and particularized injury to themselves.
In addition to initiating litigation, Congress also occasionally seeks to intervene in preexisting litigation. In cases in which the executive branch has declined to defend a federal statute from a constitutional challenge, for example, congressional entities have attempted to intervene as defendants in support of the law. The Supreme Court, in INS v. Chadha, 462 U.S. 919 (1983) and United States v. Windsor, 570 U.S. 744 (2013), has allowed Congress to intervene to defend a law that the executive branch has declined to defend but still enforces. Nonetheless, neither case resolved whether significant exceptions to this rule exist, let alone explored what rules are in place when the President both declines to defend and enforce a federal law. Moreover, in cases that do not involve the executive branch's refusal to defend a federal statute, Congress's ability to intervene as a full party to the case may be more circumscribed.
Even when Congress lacks standing to initiate or intervene in a federal lawsuit as a full-fledged party, Congress may still play a role in litigation by participating as an amicus curiae, or "friend of the court." Courts frequently allow Members, houses, and committees of Congress to file amicus briefs in support of (or opposition to) particular parties or positions.