The biggest drawback of the need for large amounts of money to campaign is that

The biggest drawback to the need to finance a political campaign with large sums of money is that it favors the participation of wealthy candidates and it excludes the non-wealthy from political participation.

Explanation:

In some political systems like the United States, candidates who want to run for public office need to also fundraise in order to have the money to produce campaign materials and to canvass for support among voters. This puts wealthy people at an advantage because they can finance their own campaigns to some extent, and they also tend to have connections with other wealthy donors who can help finance their bid for office.  Candidates who are not wealthy have less opportunity to run for office because they lack the connections to powerful people and they lack the funds to jumpstart their campaigns.  

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there are isolated pockets of farming, generally around rivers and oases, which are used for irrigation.