Pelosi is calculating that, if the election is about the issues that are on the table now, the Democrats will win. To the contrary, the surest way to lose is to impeach the president.
She can’t just come out and say that, because too many influential Democrats want Trump impeached. She has to say something to appease them. So she says she’d like to see him prosecuted.
She knows it’s not going to happen. Not only does the Justice Department guidance forbid it while Trump is in office; as we discussed here last week, the Justice Department brass, which would have to approve charges, does not subscribe to the Mueller report’s very expansive interpretation of obstruction law. There is not a clear criminal offense; and Attorney General Barr is right that a president should not be charged unless there’s an obvious crime — you don’t want to tear the country apart over something that is merely arguable or requires a novel construction of the law.
So Pelosi is urging the thing that she knows cannot possibly happen. It at least makes her sound like she has the quantum of loathing for the president demanded by her base. She is worried the alternative would be to trigger impeachment proceedings, which Democrats cannot win because the Senate will never have the two-thirds supermajority needed to convict and remove the president. She fears that would cost Democrats a very winnable 2020 election — one in which, if they play their cards right, they might take the White House and Congress.