In 2010 an explosion at a coal mine operated by Massey Energy killed 29 men. In 2015 Don Blankenship, the company’s former C.E.O., was sent to prison for conspiring to violate mine safety standards. In 2018, Blankenship appears to have a real chance at becoming the Republican candidate for senator from West Virginia.

Blankenship is one of four Republicans with criminal convictions running for office this year, several of whom may well win their party’s nominations. And there is a much broader list of Republican politicians facing credible accusations of huge ethical lapses who nonetheless emerged victorious in G.O.P. primaries, ranging from Roy Moore to, well, Donald Trump.

To be sure, there have been plenty of crooked Democrats. But usually the revelation of their crookedness ended their political careers. What’s striking about today’s Republican landscape is that people who are obvious crooks, con men or worse continue to attract strong support from the party’s base. Moore narrowly lost in Alabama’s special election, but he received 91 percent of the votes of self-identified Republicans.

And Trump, although unprecedentedly unpopular for a president at this stage of his term, continues to receive overwhelming support from the G.O.P. base. Some Republican politicians have openly admitted that this makes the party’s congressional wing unwilling to hold Trump accountable for even the most spectacular malfeasance, up to and including possible collusion with a hostile foreign power.