Why won't George W. Bush talk publicly about Donald Trump? It's simple.

George W. Bush has pursued a unique path for an ex-president, all but walking away from political life.

Since leaving office in 2009 , Bush has made his mark as a book author, the head of an institute based in Dallas , and even as a portrait painter.

Friends and associates said he is standing by his pledge not to critique other presidents and political leaders.

Friends and associates say there's no real reason for Bush to engage in politics.

The former president does speak out frequently on policy issues, mostly through his work with the George W. Bush Presidential Center at Southern Methodist University in Dallas .

Bush has hosted dozens of fundraisers for favored Republican candidates.

He has also pursued a non-traditional pastime: painting.

Cohen : Bush has prospered with public opinion even though his Republican successor, Trump , rejected many of his policies.

"He moved on from politics, and in an age when everything is political, that’s earned him respect," Cohen said.

For his part, Bush still likes to joke that historians are still debating aspects of "the first George W" - George Washington .