COPENHAGEN — An exchange in a recent debate on national TV was emblematic of changing times in Danish politics. An 18-year-old high school student named Jens Philip Yazdani was pitted against Martin Henriksen, a member of Parliament for the far-right Danish People’s Party who is the chairman of an important parliamentary committee on immigration, integration and housing. When Mr. Yazdani asserted his Danish identity as someone born and brought up in Denmark, Mr. Henriksen interrupted him.

“This is not how one becomes Danish,” he said, starkly forcing to the fore the old question of what is “Danishness.” In that moment, the nationalist politician signaled an end to the uneasy truce that has long defined the immigration debate in Denmark. By rejecting the very possibility of ever “becoming” Danish, even down several generations, he effectively shelved the political project of integration of immigrants.

“One can’t say that just because one brings the whole world to Denmark,” Mr. Henriksen went on, “and they then get some children, that those children become Danish. This is a simplification of the debate, and one that is insulting to those generations that have built this land.”

What surprised many viewers is that in an earlier era, Mr. Yazdani would have been considered a poster boy for successful integration. Born to a Danish mother and an Iranian father, he speaks Danish fluently and is the chairman of his school council. Being a meaningful contributor to society was once deemed valuable in Denmark, enough to provide a sense of belonging. But now, apparently, it’s the bloodline that matters.