On Wednesday, former Bush White House senior officials Karl Rove and Harriet Miers reached an agreement with the House judiciary committee to provide testimony about the administration's involvement in the politicised firings of US Attorneys. Though the justice department's internal investigation has already concluded that the administration's actions were inappropriate, judiciary chairman John Conyers had sought for some time, often with colourful language, to get Rove at the witness table in front of him.

The news that Rove and Miers will testify was met with cautious cheers on the left. Those who had been pushing for their testimony were pleased that an agreement was reached, but concerns still remain about whether the accord will have enough teeth to compel all necessary testimony. If it works, it may well serve as a template for interviewing former White House officials about other Bush-era scandals. But if it fails – as seems likely – it will serve as an obstacle, not a conduit, to uncovering the full truth of the last eight years.

A close reading of the three-page document outlining the agreement seems to suggest plenty of wiggle room for Rove and Miers. Their initial conversations with the committee will be private interviews, done out of the view of the public. Transcripts of the interviews will be created and provided to all "involved parties", though it's unclear if any of those parties will provide, or be allowed to provide, those transcripts to the press. The committee also explicitly reserves the right to seek public testimony, although it's equally unclear whether the parties will be compelled under the agreement to respect that right. After all, the agreement only grants the committee the right to seek public testimony, not compel it.

The scope of the testimony will be limited to facts surrounding the firings of US attorneys and, in Rove's case, issues involving the prosecution of former Alabama governor Don Siegelman. Rove and Miers will be allowed to refuse any questions that fall outside that narrow scope. But those won't be the only questions that Rove and Miers will be able to avoid.

According to the agreement, "counsel will direct witnesses not to respond to questions …when questions relate to communications to or from the president." The Bush administration may have loosened its definition of executive privilege to some extent, no longer arguing that any testimony from senior officials need be off-limits. But by allowing Rove and Miers to avoid discussing any material related to presidential communications, the former administration may have found the compromise they'd been hoping for: one that looks good on paper, but has very little impact.

There are several questions that the committee will almost certainly fail to get answered as a result. Can you describe the president's involvement in the decision to fire the US attorneys? Did you ever have a conversation with the president where he suggested firing US attorneys? Did the president order you to take action that would result in the firing of US attorneys for political reasons? If the president didn't play a role in the firings, then it would appear his team had "gone rogue", acting entirely outside his authority. And if, as has been widely speculated, he did play a role, this agreement ensures that we will never find out.

There can be no doubt that the scope of the agreement is broad enough for Congress to gather new, potentially valuable information from Rove's and Miers's testimonies. But by allowing the duo to avoid telling the full and unrestricted truth, the judiciary committee might well regret the precedent it is setting – one that will prevent a full accounting of Bush-era sins, leaving a critical part of American history hidden forever from our view.