What are Frank Underwood's ambitions?: House of Cards

Spoilers here: The Netflix series House of Cards (2013) continues to hold my interest despite its uneven pace; now through episode 8 (of 13). A number of differences between this and the British original with Sir Ian Richardson, from the 1990s, three of which are striking: much stronger role for the politician (Rep Frank Underwood)'s wife, played very well by the ice-cold Robin Wright; somewhat less of a prominent role for the young journalist, Zoe Barnes, played very well by the very well-cast Kate Mara; and actually less of a politically ambitious and manipulative role for Underwood himself, played by the always excellent Kevin Spacey. The journalist doesn't even appear in episode 8; in the British original Richardson creatively used and manipulated the journalist to plant stories in the press that advanced his personal ambitions - that's much less a driving force here; Undersood/Spacey achieves his goals through his own machinations, as well as through some sleazy dealings with campaign contributors on the part of his wife. There's a pretty elaborate subplot about Congressman in recovery running for the governorship of Pa., but it's not entirely clear that this campaign is really necessary to Underwood's success. Most striking of all in the series is the absolute utter lack of sexual sparks or passion between Underwood and wife Claire or between Underwood and journalist Zoe - these are the most nonsexual sex scenes I've ever seen. In episode 8, we get the key to that mystery, as Underwood, drunk, makes a serious pass at one his old college buddies - a bit of Brokeback Mountain here, but in this case his wife is obviously in the know and tolerant of his alliances, as his public position advances her career and leaves her free for an affair with an insipid British photographer whose work obviously echoes the great Sebastio Salgado but in a cliched and melodramatic way - glorying in the suffering of oppressed people, it seems. The series would be stronger if Underwood's ambitions were more scripted and developed; in the British, it was clear that Richardson wanted to be PM - they writers there had the advantage of a Parliamentary system, where ascension doesn't require the same sort of national campaign that takes years to develop in the U.S. Underwood seems to want to be Speaker, which makes sense - you need only the votes of your caucus  - but he doesn't really focus on this so at times he seems just like any member reasonably powerful of Congress rather than like an extremely conniving, manipulative, even corrupt member of the club.