Most capital market transactions take place on the secondary market. On the primary market, each security can be sold only once, and the process to create batches of new shares or bonds is often lengthy due to regulatory requirements. On the secondary markets, there is no limit to the number of times a security can be traded, and the process is usually very quick. With the rise of strategies such as high-frequency trading, a single security could in theory be traded thousands of times within a single hour. Transactions on the secondary market do not directly raise finance, but they do make it easier for companies and governments to raise finance on the primary market, as investors know that if they want to get their money back quickly, they will usually be easily able to re-sell their securities. Sometimes, however, secondary capital market transactions can have a negative effect on the primary borrowers: for example, if a large proportion of investors try to sell their bonds, this can push up the yields for future issues from the same entity. An extreme example occurred shortly after Bill Clinton began his first term as President of the United States; Clinton was forced to abandon some of the spending increases he had promised in his election campaign due to pressure from the bond markets [source?]. In the 21st century, several governments have tried to lock in as much as possible of their borrowing into long-dated bonds, so they are less vulnerable to pressure from the markets. Following the financial crisis of 2007–08, the introduction of quantitative easing further reduced the ability of private actors to push up the yields of government bonds, at least for countries with a central bank able to engage in substantial open market operations.