The far-right Alternative for Germany party was poised for a banner year.

Not long ago, the party, known as AfD, was polling nationally near 25 percent. With elections approaching for the European Parliament and in three eastern states — its traditional stronghold — the party looked set to achieve its chief goal of moving from the margins to the mainstream.

Suddenly, the party’s future seems murkier. It is still riding relatively high — the second-most popular party in the country. But recently, as members have been caught up in spying and influence peddling scandals, secret discussions about deporting immigrants and controversies over extreme statements, the AfD has faced a stiffening backlash, threatening the inroads it had made into the mainstream.

The steady drumbeat of missteps and scandal has forced the party, already officially labeled a “suspected” extremist group by the German authorities, to cast aside even some important members and caused fellow far-right parties abroad to shun it.

“This week that is behind us was not a good week,” Alice Weidel, one of the two leaders of the party, said at a campaign stop on May 25.

The AfD is feeling the repercussions. Local elections in the eastern state of Thuringia last weekend did not produce the resounding mandate it had hoped for, though it still finished strong.