WASHINGTON — A succession of Republican retirements from Congress, including two announcements this week, is the latest sign of a sour mood in the party about its chances to win back the House in 2020. Party operatives believe even more departures are to come.

Thirteen House Republicans of nearly every stripe — moderates and conservatives, relative newcomers and those with decades of seniority, two of the party’s 13 women and its only African-American lawmaker — have all announced their retirements in the past several weeks.

Only a few, such as Representative Will Hurd of Texas, appeared likely to face a difficult re-election campaign. Most have explained their planned farewells at the end of their terms in 2021 in personal terms, citing health and family concerns or a general sense that “it’s time.’’

But former lawmakers and several political strategists said the departures were more likely a consequence of two dawning realities for Republican House members: Being in the minority is no fun, and their chances of ending Democratic rule next year are fading fast.