It might clarify what else is going on to notice that the Democratic leadership wants us to accept that Prime Directive B requires us to have a divisive debate about a whole bunch of things; while Prime Directive A still forbids us from having a divisive debate about social policy.
Democrats say we now must take the "political risk" of Trump being re-elected and the Republicans controlling the legislature, via a prolonged and divisive debate over such things as Adam Schiff's interpretation of the oath of office, the emoluments and bribery clauses, the need to arm Kiev without any delay, the need to recognize and confront "Russian aggression" in Ukraine and Georgia and to expand NATO, the dismissal of Ukrainian interference in the 2016 election, the parsing of overheard telephone calls, and the meaning of the word "though." All that matters.
But we still cannot and must not tolerate a sharp debate about whether Americans should have healthcare, education, jobs, housing, and forgo regime-change war. That doesn't matter.
One set of things matters, and merits risking division and electoral failure. One doesn't.
Seeing what actually matters to the Democratic Party and what doesn't discloses the governing principle and the actual logic underlying the seemingly contradictory Directives. Though he is presented as the main focus in both cases, what matters is not Donald Trump. He is the most garish puppet in their Punch and Judy show, but it is not about him. What matters is maintaining neo-liberal capitalist ("centrist") domestic socio-economic policies and neocon, imperialist foreign and military policies. Both Prime Directives are based on that.
The real point of Prime Directive A is, exactly as Nancy Pelosi said, to "focus" the Party "on pursuing center-left policies"--i.e., to channel all discussion, and our undivided attention, away from insurgent social democratic and antiwar demands. For that purpose, the nomination of a candidate like Bernie Sanders or Tulsi Gabbard is the fundamental threat, and the frightening specter of a re-elected Donald Trump is held out to prevent it.
In light of that main objective, the real point of Prime Directive B is not contradictory, but complementary, to Directive A: To use attacking Trump as a means to ensure that the US continue "pursuing center-left policies." In the realm of foreign policy that means reactionary "Washington consensus" exceptionalism and interventionism, and an insistence on the dangerous anti-Russia campaign that Democrats and Republicans have been pursuing at least since Bill Clinton decided to bring virtually every post-Soviet state into NATO. For that purpose, the scary, absolutely delusional, specter of "all roads lead to Putin" Trump that the Democrats have spent three years concocting via Russiagate and its extension, Ukrainegate, is held out again as the villain that has to be stopped--this time by an "undivided" coterie of Congressional constitutionalists.
Trump in this is a foil for reinforcing the imperialist paradigm. Behind all the blather about "constitutional duty" addressed to its gullible constituency, the Democratic leadership, which knows very well the enormous political risk that impeachment hearings will help Trump, is building a case for its other real audience--Republican senators. It is publicly--and I guarantee, privately--pounding on the theme of Trump as not a reliable steward of US imperialism.