A nationalist Turkish leader said Tuesday he can't tolerate the US president's lack of courtesy in calling on Turkey to reckon with its past, resolve its dispute with Armenia and reopen their shared border. Devlet Bahceli's remarks underline the difficulties in overcoming decades of antagonism with Armenia rooted in WWI-era killings. Turkey's mass expulsion of Armenians during World War I - which Armenians say was part of a genocide that claimed 1.5 million lives - is rarely discussed in Turkey or taught in schools. But it is increasingly becoming a topic as Turkey becomes more open on the road toward European Union membership. President Barack Obama avoided the term "genocide" when he addressed Turkish lawmakers Monday about the bloodshed in the final days of the Ottoman Empire. Turkey rejects the view that there was a systematic campaign to wipe out the Armenian population.