This is a big deal that places the Comey session on a short list of congressional hearings deemed worthy of live airings on broadcast television - a list that includes the Army-McCarthy hearings in 1954, Watergate hearings in 1973, Iran-contra hearings in 1987, Anita Hill-Clarence Thomas hearings in 1991 and Clinton impeachment hearings in 1998.
The drama is undeniable. Senators surely will ask Comey about private conversations he had with President Donald Trump - specifically one in which the president reportedly said "I hope you can let this go," referring to an FBI investigation of former national security adviser Michael Flynn. How did Comey interpret that remark? Was Trump merely stating his desired outcome or pressuring the director to end the probe?
To put it more bluntly: Does Comey believe the president obstructed justice?
The networks do not want to miss Comey's answer to that key question - or any other significant moment. Yet they are typically loathe to interrupt regular programming and to forfeit the accompanying ad revenue.
It always has been that way. The Army-McCarthy hearings yielded one of the iconic lines in American politics: "Have you no sense of decency, sir?" But by the time Army lawyer Joseph Welch spoke those words to Sen. Joseph McCarthy, R-Wis., on June 9, 1954, only ABC and the now-defunct DuMont network were still airing live coverage.
The hearings dragged on for 36 days, and NBC bailed after two, citing lost ad revenue. CBS was unwilling to bump its daytime programming at all.
The Watergate hearings stretched from May 17 to Aug. 7, 1973. ABC, NBC and CBS went live for five days before deciding that non-stop coverage was unsustainable. After that, they agreed to rotate live telecast duties so that each network would lose ad revenue every third day, instead of every day.
By 1998, when the House Judiciary Committee held impeachment hearings for President Bill Clinton, the networks were even less inclined to disrupt regular programming.
"We're still waiting for details on the hearings, but my guess is that MSNBC will do gavel-to-gavel coverage, and NBC will carry key testimony live," NBC News Vice President Bill Wheatley told the Los Angeles Times in October of that year, as the networks wrestled with coverage decisions.
A month earlier, the networks had aired four hours of taped grand jury testimony by Clinton, uninterrupted by commercials, and the broadcasts had cost each of the "Big Three" about $1 million in lost revenue, the L.A. Times reported. With the advent of cable news channels, the broadcast networks felt less duty-bound to break into their scheduled shows. They ultimately did what Wheatley predicted, airing live coverage of key testimony but not every minute.
The public portion of Comey's testimony is scheduled to last only three hours; he will provide additional testimony in a closed session later in the day. We're not talking about a Watergate-level sacrifice of time and money on the part of the networks.
Still, it takes a major news event to compel the networks to go live from a congressional hearing room. Their willingness to do so for Comey is a testament to their belief that Thursday could be a historic day.