The fact is that Kilpatrick and Dahlgren were both loose cannons. While their fantasy version of the raid might have included shooting Davis and the rest of the confederate cabinet, there's not the faintest resemblance of a smoking gun that says that Lincoln or, in fact, anyone above Kilpatrick, gave such an order. Meade's investigation came to the same conclusion.
Stoneman's raid to capture Davis failed, as did Butler's. Gen. Meade wrote his wife about Kilpatrick's denial and the authenticity of the papers, stating 'I regret to say Kilpatrick's reputation, and collateral evidence in my possession, rather go against this theory.' Previously Meade had written her about the plan stating '[t]he undertaking is a desperate one', and that 'the anxiety and distress ... of the authorities at Washington is so great that it seems to demand running great risks for the chances of success.' John C. Babcock [liaison officer at Meade's headquarters] wrote, '[l]etters found on Dahlgren's body published in Richmond papers ... [are an] Authentic report of contents.' Capt. John McEntee, who accompanied Dahlgren stated, 'the papers are correct that were found upon Dahlgren, as they correspond with what Dahlgren told him.'
Those are Union officers verifying the contents of the Dahlgren Papers - we already know that previous raids failed, and that both Dahlgren and Kilpatrick met with Lincoln separately. After meeting with Lincoln Dahlgren wrote his father acknowledging the upcoming event but could not disclose the details, he would either be a hero or dead.
The Dahlgren Papers were photographed before being forwarded, later the originals were destroyed by Lincoln's crony Stanton.