ISLAMABAD — Pakistan's Prime Minister Nawaz Sharif is trying hard to put on a brave face, even as his nuclearized country's opposition politicians agitate increasingly loudly for his resignation.

A series of opposition-sponsored street rallies calling for the prime minister to quit may have done little immediately to weaken Sharif's government, which rode to power almost 30 months ago on the back of a landslide victory.

But Sharif's vulnerability is growing: At its root is not only in his inability to outwit his political foes, but more important, his failure to improve Pakistan's grim economic outlook.