Gallup tracking poll shows the decline in President Obama's approval numbers over the last 3 quarters.

The HIll:

Obama averaged a 47.9 percent approval rating for his 18th quarter in office, running from April 20 to July 19. That's down from 49.7 percent in the first quarter of Obama's second term in office, and down from 51.9 in the 16th quarter, when he was reelected.

The president got a slight boost in the early stages of the 18th quarter after the Boston Marathon bombings, but declined steadily from there and has not topped the 50 percent mark in almost a month.

According to Gallup, Obama's average for the quarter is typical for second term presidents. The president comes in well below former presidents Dwight Eisenhower, Ronald Reagan and Bill Clinton, well above Lyndon Johnson and Richard Nixon, and is near in approval to Harry Truman and George W. Bush.

Bush was at 47.3 percent for the same quarter during his second term in office, but he and Truman finished their second terms with some of Gallup's worst approval ratings on record.

"Historically, the trend has been for presidents' approval ratings to decline in their 19th quarters in office," Gallup editor-in-chief Frank Newport wrote. "Five of the seven presidents to date serving a 19th quarter saw at least some decline in their approval ratings."

The president's best quarter was his first in office, when he notched a 63 percent approval rating, while he bottomed out at 41 percent in 2011 during the debt limit negotiations with Congress.

The approval numbers come as Obama readies to press lawmakers on the economy and immigration reform this summer and as the administration prepares to rollout his signature healthcare reforms. 

Those falling numbers explain why Republicans in the House are relatively unconcerned that their stance on immigration reform will hurt them. It's not an issue that ranks high in importance according to the polls, and several elements contained in the bill are not very popular anyway.

Obama's personal approval will likely contrinue to go down, making any push to raise the debt ceiling a lot harder for him.