This piece was originally published on Just Security, an online forum for analysis of U.S. national security law and policy.

President Donald Trump’s retaliation against Speaker Nancy Pelosi’s efforts to postpone the State of the Union invitation—denying Pelosi’s use of military aircraft to travel to Afghanistan—must be understood in its historical context and for its constitutional significance. While this dispute has largely been covered as another twist in a tit-for-tat cycle of retribution, it represents a far graver abuse of power than a political spat. Trump’s interference in congressional travel misused the commander-in-chief power for political purposes, endangered the speaker’s delegation, and obstructed the exercise of Congress’ Article I legislative fact-finding responsibilities.

As a House national security subcommittee staffer, I used to organize and accompany congressional delegations, or CODELs, and staff overseas fact-finding trips—including four to Afghanistan during Pelosi’s previous speakership. Having also served in the White House Counsel’s Office, I have published on the specific topic of CODELs as an important arena for interbranch relationships. I know from experience. Trips into combat zones are logistically complicated multiagency and interbranch operations with ever-present security concerns. This most recent confrontation exposes long-held executive-legislative tensions. But Trump’s acts are wholly unprecedented and dangerous departures from historical practice—not to mention his obligations as the nation’s chief executive.

On Jan. 16, Pelosi sent a letter to the president citing difficulties in ensuring adequate security for a State of the Union speech before a joint session of Congress due to shutdown strains on federal agencies and employees. Pelosi suggested that Trump instead provide a written submission (as was done in the early days of the republic) or conduct the speech as an Oval Office address. Many accepted Pelosi’s security rationale, others viewed Pelosi’s letter as an effort to deny Trump the traditional SOTU megaphone and pageantry.

Within 24 hours, Trump sent a letter to Pelosi, which White House press secretary Sarah Huckabee Sanders tweeted, informing the speaker that the president was withdrawing military aircraft authorization for her CODEL:

Due to the Shutdown, I am sorry to inform you that your trip to Brussels, Egypt, and Afghanistan has been postponed. We will reschedule this seven-day excursion when the Shutdown is over. In light of the 800,000 great American workers not receiving pay, I am sure you would agree that postponing this public relations event is totally appropriate. …Obviously, if you would like to make your journey, that would certainly be your prerogative.

That last line echoed Pelosi’s comment about the SOTU that “He can make it from the Oval Office if he wants.” Adding to the insult, the White House reportedly did not inform the members of Congress slated to travel on the CODEL until 30 minutes before they were scheduled to go wheels up. The legislators were sitting on a U.S. Air Force bus when they found out.

Congressional members and staff have been severely attacked and killed during foreign travel.

Afterward, Pelosi’s chief of staff Drew Hammill tweeted out more details about the canceled trip. After noting there was no Egypt stop planned, Hammill tweeted: “The purpose of the trip was to express appreciation & thanks to our men & women in uniform for their service & dedication, & to obtain critical national security & intelligence briefings from those on the front lines.” He also noted that the Brussels stop related to mandatory flight crew rest given the distances involved in travel to South Asia (a required stop in Europe or North Africa is consistent with my trip planning experience), and therefore the CODEL was slated to make use of that time on the public’s behalf to meet with representatives of NATO allies.

Trump’s letter was not only unprecedented in its use of commander-in-chief authority to ratchet up a political dispute, but it also revealed itinerary plans that had not been publicly released because of security concerns.

In the wake of Trump’s letter and revelation about trip details, Pelosi accused the president of endangering the travelers to the point the trip could no longer proceed even by commercial air travel. According to Pelosi, the State Department’s diplomatic security service informed her office that it was too dangerous to fly to Afghanistan by commercial air after all the publicity. She told reporters:

We weren’t going to go because we had a report from Afghanistan that the President outing our trip had made the scene on the ground much more dangerous because it’s just a signal to the bad actors. … You never give advance notice of going into a battle area. You just never do. Perhaps the President’s inexperience didn’t help him understand that protocol. The people around him, though, should have known that, because that’s very dangerous.

These are not idle security concerns. Congressional members and staff have been severely attacked and killed during foreign travel. A few examples:

• Rep. Lawrence Patton McDonald, D-Georgia, was among those killed when the Soviet military shot down Korean Air Lines Flight 007 on Sept. 1, 1983.

• Rep. Leo Joseph Ryan, D-California, was gunned down on an airstrip in Guyana by cult members in the Jonestown massacre in 1978. Current Rep. Jackie Speier, D-California, who accompanied Ryan as congressional staff on that trip, was shot five times in the attack.

• Harold “Hal” W. Rosenthal, a Senate Foreign Relations Committee staff member, was killed in a 1976 terrorist bombing in Istanbul while he was overseas on a congressional staff trip to Israel.

Security is a paramount concern for the speaker of the House as third in the line of succession to the presidency. The speaker would be a highly valuable target for a terrorist network. She should have travel support resembling the president and vice president in order to accommodate her security detail and communications technicians—especially when traveling into combat zones.

The second half of Hammill’s statement about the trip’s purpose—“to obtain critical national security & intelligence briefings from those on the front lines”—is of fundamental and, indeed, constitutional importance. Congress was engaging in overseas travel to further its legislative power of inquiry in order to inform policy judgments. In McGrain v. Daugherty, the Supreme Court explained that congressional power to conduct inquiries is implied by the Constitution’s grant of legislative power in Article I. The court correctly noted: “A legislative body cannot legislate wisely or effectively in the absence of information respecting the conditions which the legislation is intended to affect or change.” What’s more, as the court observed in Barenblatt v. United States, the “scope of the power of inquiry … is as penetrating and far-reaching as the potential power to enact and appropriate under the Constitution.”

Far from a mere “public relations event,” as Trump characterized Pelosi’s trip, these initiatives provide critical information to senior policymakers responsible for authorizing use of force, appropriating funds, and establishing military regulations. To be sure, congressional travel can be abused by triviality or extravagance. But CODELs to combat zones allow our troops to see policymakers taking the risks and the time to visit them and hear from them. This trip would have also demonstrated American respect for—and presented an opportunity to hear from—Afghan partners on the ground. My travel companions and I learned a massive amount of information useful to our investigations and policy mandates on our trips to Afghanistan and other hot spots. For examples of our reports informed by overseas congressional travel, see “Warlord, Inc.: Extortion and Corruption along the U.S. Supply Chain in Afghanistan” and “Mystery at Manas: Strategic Blind Spots in the Department of Defense’s Fuel Contracts in Kyrgyzstan.”

Here, the president intentionally interfered with that function in an act of political retaliation. At a minimum, he set back any safe travel to Afghanistan by the speaker for the near future.

Even under normal circumstances, congressional travel creates tensions between the branches. Last year I wrote a short law review article for a symposium on congressional oversight that addressed legal and practical challenges facing Congress as it engages in fact-finding overseas. In a section describing some of those practical challenges, I wrote about congressional reliance on the executive branch as an especially important area of concern:

There are a few other practical challenges to conducting effective oversight beyond U.S. borders that are worthy of brief mention. In many cases, congressional and staff fact-finding trips are essential to conducting penetrating oversight. Depending on the subject matter and location, congressional investigators may require transcription and translation services, embassy workspace, security, and in-country travel support. Congress is reliant on the good offices of the State Department control officers assigned to the delegation, and, in combat zones, the Department of Defense. These personnel deployed overseas have broad important portfolios beyond staffing congressional travel, and legislative travelers should be mindful of their burden on the mission. In addition, there is often an awkward dynamic in which the congressional delegation is conducting oversight over the very departments that are hosting it. At times, the executive branch tries to dictate the legislative branch’s trip agenda, which is not the appropriate dynamic. Therefore, there can be seemingly endless negotiations about access to sites, foreign government officials, combat zones, and various services.

I then encouraged Congress to codify executive branch travel support obligations:

Congress should pass legislation that formalizes its expectations of executive branch support for oversight travel. This legislation should not impose too many onerous obligations on Embassy or military staff. However, statutory mandates for facilitation of congressional oversight on transcription, translation, workspace, in-country mobility, and security could clarify interbranch relations and improve efficiency. Moreover, it could present an opportunity for Congress to codify an expression of the importance of its autonomy in setting its oversight agenda when traveling abroad.

I saw congressional reliance on executive branch travel support as a function of interbranch comity as problematic, because it gave the executive branch too much leverage over the CODEL agenda. My concerns, borne of experience, related to heavy-handed scheduling negotiations with the embassy staff or requests by the military to embed a general officer on the trip as a minder.

Those concerns seem quaint now. I never contemplated the president of the United States abusing commander-in-chief powers to obstruct congressional travel. It is now clear that Congress will have to codify executive branch travel support obligations and otherwise engage in self-help in order to ensure it can engage in critical fact-finding overseas. But the president’s misconduct transcends interbranch tensions or rank politics. Rather, by engaging in petty political retribution, he’s trampled on constitutional obligations in two branches of government.

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