ANd the GOP managed to win the House in 2010 doing nothing but running against Obama.
That's the GOP - they're appealing to an entirely different demographic, one where "vote against the n-word" is going to work just fine.
I think the Don just does not get that US politics is different the UK politics..it's a lot rowdier and is often driven by dislike of the other party.
I may not get US politics, who knows, but successful Democratic Party candidates in the modern era have been young and have been absolute rock stars. Both Bill Clinton and Barack Obama are excellent orators, but more than that they had something about them which inspired the electorate.
The unsuccessful candidates, Dukakis, Mondale, Gore, Kerry and Hillary were all arguably highly competent legislators, smart people who would be willing to work hard for the American people, but they completely lacked the *it* factor to get Democratic Party voters out in force.
IMO Democratic Party voters want to be wooed into voting for the candidate. GOP voters are far more reliable, though in their case they seem to want someone they can relate to, and have a beer with, Reagan, George W Bush, Donald Trump and are less worried about personality.
George H W Bush is an outlier but I'd say he was Reagan's third term and as soon as he was "rumbled", he failed to be reelected.
His list of outcomes in November is also limited;like a scenario in which the Dems do not win the house but come within four or five seats of doing so,giving them a de facto ablity to block most legislation.
As other posters have pointed out, the ability merely to block legislation may actually backfire on the Democratic Party. GOP voters may be perfectly happy for their representatives to be wholly obstructionist, after all Conservatism should be about preserving the status quo so stopping new legislation is a good second best to getting your own legislation through. Progressives want change so will be turned off by the Democratic Party becoming 100% obstructionist.
In any case, IMO it would just result in President Trump and his administration increasingly resorting to rule by executive order and/or underfunding - neither of which is a good thing.