The word “timber” has meant “a personal quality or character” since at least 1612. Political “timber” has long been spoken of in American politics.
 
The term “political timber” has been cited in print since at least 1801, “gubernatorial timber” has been cited in print since at least 1831, “Congressional timber” has been cited in print since at least 1838 and “Presidential timber” has been cited in print since at least 1847.
 
   
(Oxford English Dictionary)
timber, n.
fig. Bodily structure, frame, build. In later use, the ‘stuff’ of which a person is made; personal quality or character; preceded by a qualifying word: suitable quality or character for the specified office, etc. Cf. material adj. 3. Chiefly U.S.
1612 G. Paule Life Whitgift §138. 93   For his small timber, he was of a good quicke strength, straight and well shaped.
1613 F. Beaumont Knight of Burning Pestle ii. sig. D3v,  The twelue Companies of London cannot match him, timber for timber.
1670 Milton Hist. Brit. vi. 265   Canute‥doubting to adventure his body of small Timber, against a man of Iron sides.
1822 C. Lamb Some Old Actors in Elia 1st Ser.,  He was not altogether of that timber out of which cathedral seats and sounding-boards are hewed.
1892 Chicago Tribune 4 Apr. 4/5   Senator Cullom of Illinois is better Presidential timber than was generally supposed.
1914 Emporia (Kansas) Gaz. 13 Jan. 2/1   He is everlastingly‥N.G. as gubernatorial timber.
     
9 April 1801, Windham (CT) Herald, pg. 3:
What a supply of political timber the democratic part of Connecticut must afford, when in making up a catalogue of five public officers, they are obliged to purloin two from the Federalists to make their men go down at all?
 
8 July 1809, Suffolk (NY) Gazette, pg. 3:
May the political timber of the United States so celebrated when first cut, be durable in the estimation of a congressional caucus.
 
24 March 1831, Sun (MA), pg. 3:
Massachusetts does not appear to be deficient in “Gubernatorial timber!”
 
10 August 1833, Norfolk (MA) Advertiser, pg. 2:
GUBERNATORIAL TIMBER.
 
20 September 1838, Sun (MA), pg. 2:
The whigs are in a terrible stew about a candidate for Congress. They have plenty of “Congressional timber,” but it does not work to good advantage, and they are afraid of a loss.
 
1 December 1847, New York (NY) Spectator, pg. 1: 
A fearful lack of Presidential timber there must be, when such a man as Sam Houston is put forward for that high office.
 
30 October 1851, Sandusky (OH) Register, pg. 2:
WILLIAM L. MARCY, of New York, is named as a candidate for the Presidency. The Democracy are not likely to experience any scarcity of Presidential timber.
 
21 May 1852, Cleveland (OH) Plain Dealer, pg. 2, col. 1:
There is Presidential timber enough in the Democratic party of these United States to stock the earth with Republics, and which duty some day or other will fall upon the American Democratic party to do, either by procy or in propia persona.
 
OCLC WorldCat record
Presidential timber; a history of nominating conventions, 1868-1960.
Author: Herbert Eaton
Publisher: [New York] Free Press of Glencoe [1964]
Edition/Format:  Book : English
 
OCLC WorldCat record
From Mighty Oaks to Little Acorns: The Problems of the Presidential Timber Business
Author: Michael Foley
Edition/Format:  Article : English
Publication: Journal of American Studies, Apr., 1990, vol. 24, no. 1, p. 85-92
Database: JSTOR
 
Real Clear Politics
February 14, 2010
Is Palin Presidential Timber?
Dan Balz, Washington Post
Sarah Palin has proved that she can draw a crowd. What she has yet to demonstrate is that she can translate the appeal of a phenomenon into a political force that can attract or mobilize sizable numbers of voters.
 
The former Alaska governor is the Republican Party’s biggest celebrity. She has given voice to a grass-roots movement grounded in anger with Washington and President Obama’s policies. But her political future remains in question. Is she presidential timber?