Breakdown of Başkanın tasarıyı veto edeceğine dair bir iddia var.
bir
a / an
var
there is / existent
başkan
president, chairman
iddia
claim
Questions & Answers about Başkanın tasarıyı veto edeceğine dair bir iddia var.
How does edeceğine dair work here to mean "that [he] will veto"?
This is the core structure for saying "about/regarding the fact that...". First, we take veto etmek and add the future nominalizer -ecek because the veto is in the future. Then we add the 3rd person possessive -i (making it edeceği) to match the subject (başkanın). Finally, we add the buffer -n- and the dative case -e (edeceğine) because the postposition dair always requires the dative.
Why is the subject başkanın in the genitive case instead of just başkan?
In Turkish subordinate clauses like the one created by -ecek here, the subject of the clause takes the genitive case. You can think of it literally as "the president's future-vetoing". The genitive başkanın pairs with the possessive ending on edeceğ-i-ne.
Could we use hakkında instead of dair in this sentence?
Yes, but you would need to drop the dative case. Dair requires the dative (edeceğine dair), while hakkında does not. If you used hakkında, the phrase would just be veto edeceği hakkında. Both mean "about the fact that...", but dair sounds a bit more formal, which perfectly fits the political context of a "claim" (iddia) and a "draft" (tasarı).