How can I redefine the leader in tocloft so that it is has a minimum length? The background is that I always want leaders in TOC to appear with at least two dots, forcing line breaks in titles if necessary. The example below is a bit silly. The problem arises more often with multicolumn TOCs.
\documentclass{book}
\usepackage{tocloft}
\cftsetpnumwidth{1em}
\renewcommand\cftdotsep{2}
\begin{document}
\tableofcontents
\chapter{This is a chapter}
\section{Medium length title}
\section{Very, very long title of a section bbb bbb bb bb bb bb b b b b b b b}
\section{Medium length title}
\end{document}
