Well i guess i mean with their goal, they believe that if we exercise their beliefs, america won't go over the same cliff as Greece (and that's where were headed), but if I had to choose from your choices i'd say national level, more of like an overall kind of thing.
Multi-laywered answer then.
First, they've already succeeded to a point. The 2010 race saw a number of Tea Party backed, and Tea Party type if not specifically backed, candidates entering into the House and the Senate. Their entrance into the House has largely helped lead a push, with questionable success at times albiet, to further their ideological agenda.
Second, they've managed to steer the focus at least somewhat for the Republican establishment and for the 2012 race towards the fiscal end of things. It's still a bit questionable about how much of a success that is since the economic issues going on would perhaps push it to the forefront as well. Still, the Republicans, by and large, since 2010 seem to have been more focused on governmental and fiscal issues and pushing the social issues less strongly. Typically, the massive social conservative talk over the past little bit has been spurred by off handed comments by primary candidates followed by the media and those on the left making it a continued issue to talk about. Strangely, it's the Left, not the right, so far this year making the most hay out of Social issues it seems. That change in the Republican party, I think, is at least a bit attributed to the Tea Party.
Third, I think they could see some success with regards to congressional elections again. That's truly where the movement is at it's best due to the nature of its operation.
Fourth, I think they will continue to have little real impact on the Presidential Election in terms of sizable support or greater voice, though a better impact then they did during the primaries. I've explained it numerous times on the forum so won't go into detail, but because of the regional and segmented nature of the Tea Party it is better situated for congressional support than Presidential support due to the ability to tailor candidates to the additional, non-tea party, concerns of that particular locations populatoin.
Fifth, in the sense of having lasting success, it's hard to say really. I think movements rarely succeed at getting everything they want, and additionally I think that once a movement gets most of what it wants and gets to the spirit of what it was pushing for they tend to transform into a disgusting misrepresentation of themselves that is based less on actual principle and more on individuals wishing to use it for power. I think ultimately the Tea Party will have some success shifting the view point of the Republican Party to a certain degree, but due to the regional nature and overlap of the movement with other conservative movements I think they'll be hard pressed to succeed at any sizable, long lasting, significant shift unless some kind of centralized political figure could come forth with enough charisma to bypass the various ideological divides between different regional tea party groups and actually unite them behind a singular presidential candidate.