Learn English – alternate phrases for “Not well thought out”

It's called a slip of the pen (more common), or slip of the keyboard (less common).

Either is fine, and will be understood. If you desire to be precise with your idioms, go ahead and use "slip of the keyboard". It's not in as many dictionaries/thesauruses, but people use it, and it makes enough sense that no one should misunderstand it.

I also agree with KeithS: typo would be fine in many cases of "slips of the keyboard", however the "slip" idioms usually indicate more of a mistake in the writer's mind (wrong choice of word) than a typing error, as with "slip of the tongue". "Typo" usually has to do with a small mistake involving a few letters, which the typist did not mean to include, whereas "slip of the pen" or "slip of the keyboard" indicates a mistake of greater scale, such as choosing the wrong word, which, at the time, the typist usually did mean to include, but later realizes his mistake.

1) trying for a consolation goal

(sports) A goal scored by the losing team near the end of a game, that has no effect on the outcome. — wiktionary.

Person A had long since won the match, and person B was reduced to trying for a late consolation goal [or score or prize].

2) Also a consolation prize has similar connotations.

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3) The Lib Dems are fighting a losing battle.