There are a number of characters in a gate and to open one you need to get them into a situation where all of these ducks are arranged linearly. The opening of a gate will result in a cycle within the news media, generating a good deal of economically valuable chaos before dying out whether or not some conclusion has been reached. Generally one or more of the characters is some important figure in government, specifically within the beltway (generally this is an American phenomenon). The media ruckus attempts to suggest that the current party in power is weakened and will try to be the 'first on the ground' to cover as much of the kerfluffle that results.
This list is the classical one and a gate may open with or without some of these members, or they may have some other position or agenda. Your mileage may vary.
The Whistleblower: An inside voice, who would otherwise be censured for leaking the Information, who 'bravely' offers the Information to some media source. They may go on to use their status as the source of this Information to pad their bank accounts in some way, going on the media circuit, writing a tell-all book, becoming a notorious editorial figure. They may be sincerely offering the Information in order to root out some Incriminatable Potentate from a position of power. Both of these facets of the personality of the Whistleblower may be the case, but in either case the reaction to the Whistleblower will be that they are acting purely out of self interest. This person is usually an insider, a loyal follower who has changed their opinion of the Incriminated Potentate. Alternately in these times characterized by vast information networks, the Information may have been stolen by wire.
The Intrepid Reporter: A brave voice of reason who chooses 'to speak truth to power.' Is offered the Information by the Whistleblower and goes public with it. Similarly may be motivated by fame and money, and the reaction to the opening of a gate will state that this motivation is the one underlying the reporter's actions whether or not they are actually acting out of avarice. Some Reporters skip the Whistleblower and retrieve the Information directly, YMMV.
The Information: A file, a ledger, a tape, evidence of the criminal nature of someone is power. This little folio of boring looking papers changes hands between the Whistleblower and the Reporter. When this happens a quiet clanking noise is heard as a latch comes off the gate before it gets blown wide open. The Information doesn't need to be true or it may have its content managed to contextualize something specific to the Whistleblower and/or reporter's agenda.
Incriminated Potentate: The center of the storm, the man who ordered the burgling of political opponents or bought and sold Floridian swamp land to an intern with a fetish for 50-somethings. This guy, and it is usually a man, will generally be arrogant, will dismiss the open gate as a trick of the light, smoke and mirrors. They will be surprised with the bulls start rushing through the gate. For weeks during and after the gate they will take on a slightly dazed look as all they worked for begins to seem fragile and prone to break at any moment. In many cases the Whistleblower knew and was friends with this glorious leader, but some event triggered their brutalization of the Potentate's image.
The Money: A trail of green, rectangular, uncooked breadcrumbs that can be followed from the Information to the Incriminated Potentate. This trail may not exist, but it can be followed either way by conspiracy theorists, who will end up on television spouting their theories.
It all starts with a midnight meeting in a dank basement car-park. The Whistleblower has found an Intrepid Reporter to appraise. They try to establish trust. The Reporter asks if he or she can trust the Information. The dishonest Whistleblower, having looked for a similarly dishonest Reporter, will dismiss the soundness of the Information as unimportant. The honest one will say something cryptic like 'Just follow the Money.'
The action will hit the news and the kerfluffle will hit the fan. The Money trail will get examined and explained on poorly constructed flow charts. Baseball and automobile analogies will be made. Someone somewhere will call this the Perfect Storm. The media will chum the waters with juicy details, and finally make the comparison to the classic gates from the history of journalism. The pundits will smell blood in the water and demand the resignation of the Incriminated Potentate.
The polls will call for a criminal case, the Justice department will launch a probe, Congress will appoint a special prosecutor. The story will roll around for several weeks. Some gates will last longer if people with vendettas are involved. Some will result in a resignation. All will involve a media frenzy. Watch your hands.