When news arose that Donald Trump Jr. personally held a meeting with Russian representatives at Trump Tower, along with Jared Kushner and Paul Manafort, Don Jr. quickly released a statement saying the meeting was about “the adoption of Russian children.” The purpose of the meeting was later revealed to be an effort dig up dirt on Hillary Clinton.

A short time after Don Jr. released his statement, the Washington Post reported that Donald Trump himself had dictated the misleading statement aboard Air Force One:

Flying home from Germany on July 8 aboard Air Force One, Trump personally dictated a statement in which Trump Jr. said that he and the Russian lawyer had “primarily discussed a program about the adoption of Russian children” when they met in June 2016, according to multiple people with knowledge of the deliberations. The statement, issued to the New York Times as it prepared an article, emphasized that the subject of the meeting was “not a campaign issue at the time.”

The claims were later shown to be misleading.

Special Counsel Robert Mueller is now seeking to interview Trump's staff who had a hand in crafting that statement. From CNN:

Special Counsel Robert Mueller's team has approached the White House about interviewing staffers who were aboard Air Force One when the initial misleading statement about Donald Trump Jr.'s meeting with a Russian lawyer at Trump Tower was crafted, three sources familiar with the conversations said.

The special counsel's discussions with the White House are the latest indication that Mueller's investigators are interested in the response to the Trump Tower meeting. Mueller wants to know how the statement aboard Air Force One was put together, whether information was intentionally left out and who was involved, two of the sources said.
Mueller's questions could go to the issue of intent and possible efforts to conceal information during an obstruction of justice investigation. The answers to Mueller's questions also could illuminate the level of anxiety surrounding the meeting and the decision-making that followed.

Emphasis added. If Donald Trump knowingly crafted a statement about the meeting with the Russians that he knew to be false, that would certainly appear to be evidence he was trying to obstruct justice and the Mueller investigation.