In this instance, it's extremely simple. It's illegal for corporations in Texas to give money to state political races. DeLay's PAC, TRMPAC, accepted corporate money and then laundered it via writing a check to the RNC stipulating which candidates should receive the money.
He of course claims ignorance to this scheme but it stands to reason that Ronnie Earle would not have indicted him if he did not possess enough evidence and/or that Earle has someone(s) who is ready to sing against DeLay. In addition, newspaper reports have already established that DeLay was very much directly involved with the corporate contributions.
And as for Ronnie Earle himself, it's already been published here and everywhere that he's prosecuted more Dems than Republicans (12 to 3 ratio!). In addition, it's been stated that every single person that Earle has indicted over the years, whether Dem or Republican, has cried foul due to politics. You can now include DeLay in that group.
The fact is liberals can only hope that new Chief Justice Roberts will be as "partisan" a judge as Ronnie Earle has been.
The most recent issue of The New Republic has some insightful things to say about this latest bit of DeLay scandal, pointing out that his indictment actually symbolizes a greater stench:
Of course, even DeLay himself is merely a cog in a Washington Republican machine that has abandoned morality in its fanatical pursuit of power. Beyond rooting for a jury in Travis County,Texas, to return a guilty verdict in the months ahead, Democrats need to make clear to the public that his indictment represents a mere fraction of the Republican Congress’s corruption. The House ethics committee, for instance, must continue to investigate Abramoff’s sleazy lobbying, which envelops several other GOP congressmen and reveals the disgusting influence K Street lobbyists enjoy over federal lawmaking.DeLay has taken the House and turned it into the revolting, decaying house in this movie. As TNR writes, "with any luck, it could be the beginning of a desperately needed fumigation of Capitol Hill."